[nbd.git] / nbd-server.c

/*
 * Network Block Device - server
 *
 * Copyright 1996-1998 Pavel Machek, distribute under GPL
 *  <pavel@atrey.karlin.mff.cuni.cz>
 * Copyright 2001-2004 Wouter Verhelst <wouter@debian.org>
 * Copyright 2002 Anton Altaparmakov <aia21@cam.ac.uk>
 *
 * Version 1.0 - hopefully 64-bit-clean
 * Version 1.1 - merging enhancements from Josh Parsons, <josh@coombs.anu.edu.au>
 * Version 1.2 - autodetect size of block devices, thanx to Peter T. Breuer" <ptb@it.uc3m.es>
 * Version 1.5 - can compile on Unix systems that don't have 64 bit integer
 *      type, or don't have 64 bit file offsets by defining FS_32BIT
 *      in compile options for nbd-server *only*. This can be done
 *      with make FSCHOICE=-DFS_32BIT nbd-server. (I don't have the
 *      original autoconf input file, or I would make it a configure
 *      option.) Ken Yap <ken@nlc.net.au>.
 * Version 1.6 - fix autodetection of block device size and really make 64 bit
 *      clean on 32 bit machines. Anton Altaparmakov <aia21@cam.ac.uk>
 * Version 2.0 - Version synchronised with client
 * Version 2.1 - Reap zombie client processes when they exit. Removed
 *      (uncommented) the _IO magic, it's no longer necessary. Wouter
 *      Verhelst <wouter@debian.org>
 * Version 2.2 - Auto switch to read-only mode (usefull for floppies).
 * Version 2.3 - Fixed code so that Large File Support works. This
 *      removes the FS_32BIT compile-time directive; define
 *      _FILE_OFFSET_BITS=64 and _LARGEFILE_SOURCE if you used to be
 *      using FS_32BIT. This will allow you to use files >2GB instead of
 *      having to use the -m option. Wouter Verhelst <wouter@debian.org>
 * Version 2.4 - Added code to keep track of children, so that we can
 *      properly kill them from initscripts. Add a call to daemon(),
 *      so that processes don't think they have to wait for us, which is
 *      interesting for initscripts as well. Wouter Verhelst
 *      <wouter@debian.org>
 * Version 2.5 - Bugfix release: forgot to reset child_arraysize to
 *      zero after fork()ing, resulting in nbd-server going berserk
 *      when it receives a signal with at least one child open. Wouter
 *      Verhelst <wouter@debian.org>
 * 10/10/2003 - Added socket option SO_KEEPALIVE (sf.net bug 819235);
 *      rectified type of mainloop::size_host (sf.net bugs 814435 and
 *      817385); close the PID file after writing to it, so that the
 *      daemon can actually be found. Wouter Verhelst
 *      <wouter@debian.org>
 * 10/10/2003 - Size of the data "size_host" was wrong and so was not
 *      correctly put in network endianness. Many types were corrected
 *      (size_t and off_t instead of int).  <vspaceg@sourceforge.net>
 * Version 2.6 - Some code cleanup.
 * Version 2.7 - Better build system.
 * 11/02/2004 - Doxygenified the source, modularized it a bit. Needs a 
 *      lot more work, but this is a start. Wouter Verhelst
 *      <wouter@debian.org>
 */

/* Includes LFS defines, which defines behaviours of some of the following
 * headers, so must come before those */
#include "lfs.h"

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/select.h>         /* select */
#include <sys/wait.h>           /* wait */
#ifdef HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif
#include <sys/param.h>
#ifdef HAVE_SYS_MOUNT_H
#include <sys/mount.h>          /* For BLKGETSIZE */
#endif
#include <signal.h>             /* sigaction */
#include <netinet/tcp.h>
#include <netinet/in.h>         /* sockaddr_in, htons, in_addr */
#include <netdb.h>              /* hostent, gethostby*, getservby* */
#include <syslog.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <arpa/inet.h>
#include <strings.h>
#include <dirent.h>
#include <unistd.h>
#include <getopt.h>

#include <glib.h>

/* used in cliserv.h, so must come first */
#define MY_NAME "nbd_server"
#include "cliserv.h"

/** Default position of the config file */
#ifndef SYSCONFDIR
#define SYSCONFDIR "/etc"
#endif
#define CFILE SYSCONFDIR "/nbd-server/config"

/** Where our config file actually is */
gchar* config_file_pos;

/** Logging macros, now nothing goes to syslog unless you say ISSERVER */
#ifdef ISSERVER
#define msg2(a,b) syslog(a,b)
#define msg3(a,b,c) syslog(a,b,c)
#define msg4(a,b,c,d) syslog(a,b,c,d)
#else
#define msg2(a,b) g_message(b)
#define msg3(a,b,c) g_message(b,c)
#define msg4(a,b,c,d) g_message(b,c,d)
#endif

/* Debugging macros */
//#define DODBG
#ifdef DODBG
#define DEBUG( a ) printf( a )
#define DEBUG2( a,b ) printf( a,b )
#define DEBUG3( a,b,c ) printf( a,b,c )
#else
#define DEBUG( a )
#define DEBUG2( a,b ) 
#define DEBUG3( a,b,c ) 
#endif
#ifndef PACKAGE_VERSION
#define PACKAGE_VERSION ""
#endif
/**
 * The highest value a variable of type off_t can reach. This is a signed
 * integer, so set all bits except for the leftmost one.
 **/
#define OFFT_MAX ~((off_t)1<<(sizeof(off_t)*8-1))
#define LINELEN 256       /**< Size of static buffer used to read the
                            authorization file (yuck) */
#define BUFSIZE (1024*1024) /**< Size of buffer that can hold requests */
#define GIGA (1*1024*1024*1024) /**< 1 Gigabyte. Used as hunksize when doing
                                  the multiple file thingy. @todo: make this a
                                  configuration option. */
#define DIFFPAGESIZE 4096 /**< diff file uses those chunks */
#define F_READONLY 1      /**< flag to tell us a file is readonly */
#define F_MULTIFILE 2     /**< flag to tell us a file is exported using -m */
#define F_COPYONWRITE 4   /**< flag to tell us a file is exported using
                            copyonwrite */
#define F_AUTOREADONLY 8  /**< flag to tell us a file is set to autoreadonly */
GHashTable *children;
char pidfname[256]; /**< name of our PID file */
char default_authname[] = "/etc/nbd_server.allow"; /**< default name of allow file */

/**
 * Variables associated with a server.
 **/
typedef struct {
        gchar* exportname;    /**< (unprocessed) filename of the file we're exporting */
        off_t hunksize;      /**< size of a hunk of an exported file */
        off_t expected_size; /**< size of the exported file as it was told to
                               us through configuration */
        unsigned int port;   /**< port we're exporting this file at */
        char* authname;      /**< filename of the authorization file */
        int flags;           /**< flags associated with this exported file */
        unsigned int timeout;/**< how long a connection may be idle
                               (0=forever) */
        int socket;          /**< The socket of this server. */
} SERVER;

/**
 * Variables associated with a client socket.
 **/
typedef struct {
        off_t exportsize;    /**< size of the file we're exporting */
        char *clientname;    /**< peer */
        char *exportname;    /**< (processed) filename of the file we're exporting */
        GArray *export;    /**< array of filedescriptors of exported files;
                               only the first is actually used unless we're
                               doing the multiple file option */
        int net;             /**< The actual client socket */
        SERVER *server;      /**< The server this client is getting data from */
        char* difffilename;  /**< filename of the copy-on-write file, if any */
        int difffile;        /**< filedescriptor of copyonwrite file. @todo
                               shouldn't this be an array too? (cfr export) Or
                               make -m and -c mutually exclusive */
        u32 difffilelen;     /**< number of pages in difffile */
        u32 *difmap;         /**< see comment on the global difmap for this one */
} CLIENT;

/**
 * Type of configuration file values
 **/
typedef enum {
        PARAM_INT,              /**< This parameter is an integer */
        PARAM_STRING,           /**< This parameter is a string */
        PARAM_BOOL,             /**< This parameter is a boolean */
} PARAM_TYPE;
/**
 * Configuration file values
 **/
typedef struct {
        gchar *paramname;       /**< Name of the parameter, as it appears in
                                  the config file */
        gboolean required;      /**< Whether this is a required (as opposed to
                                  optional) parameter */
        PARAM_TYPE ptype;       /**< Type of the parameter. */
        gpointer target;        /**< Pointer to where the data of this
                                  parameter should be written. If ptype is
                                  PARAM_BOOL, the data is or'ed rather than
                                  overwritten. */
        gint flagval;           /**< Flag mask for this parameter in case ptype
                                  is PARAM_BOOL. */
} PARAM;

/**
 * Check whether a client is allowed to connect. Works with an authorization
 * file which contains one line per machine, no wildcards.
 *
 * @param opts The client who's trying to connect.
 * @return 0 - authorization refused, 1 - OK
 **/
int authorized_client(CLIENT *opts) {
        FILE *f ;
   
        char line[LINELEN]; 

        if ((f=fopen(opts->server->authname,"r"))==NULL) {
                msg4(LOG_INFO,"Can't open authorization file %s (%s).",
                     opts->server->authname,strerror(errno)) ;
                return 1 ; 
        }
  
        while (fgets(line,LINELEN,f)!=NULL) {
                if (strncmp(line,opts->clientname,strlen(opts->clientname))==0) {
                        fclose(f);
                        return 1;
                }
        }
        fclose(f) ;
        return 0 ;
}

/**
 * Read data from a file descriptor into a buffer
 *
 * @param f a file descriptor
 * @param buf a buffer
 * @param len the number of bytes to be read
 **/
inline void readit(int f, void *buf, size_t len) {
        ssize_t res;
        while (len > 0) {
                DEBUG("*");
                if ((res = read(f, buf, len)) <= 0)
                        err("Read failed: %m");
                len -= res;
                buf += res;
        }
}

/**
 * Write data from a buffer into a filedescriptor
 *
 * @param f a file descriptor
 * @param buf a buffer containing data
 * @param len the number of bytes to be written
 **/
inline void writeit(int f, void *buf, size_t len) {
        ssize_t res;
        while (len > 0) {
                DEBUG("+");
                if ((res = write(f, buf, len)) <= 0)
                        err("Send failed: %m");
                len -= res;
                buf += res;
        }
}

/**
 * Print out a message about how to use nbd-server. Split out to a separate
 * function so that we can call it from multiple places
 */
void usage() {
        printf("This is nbd-server version " VERSION "\n");
        printf("Usage: port file_to_export [size][kKmM] [-l authorize_file] [-r] [-m] [-c] [-a timeout_sec] [-C configuration file]\n"
               "\t-r|--read-only\t\tread only\n"
               "\t-m|--multi-file\t\tmultiple file\n"
               "\t-c|--copy-on-write\tcopy on write\n"
               "\t-C|--config-file\tspecify an alternat configuration file\n"
               "\t-l|--authorize-file\tfile with list of hosts that are allowed to\n\t\t\t\tconnect.\n"
               "\t-a|--idle-time\t\tmaximum idle seconds; server terminates when\n\t\t\t\tidle time exceeded\n\n"
               "\tif port is set to 0, stdin is used (for running from inetd)\n"
               "\tif file_to_export contains '%%s', it is substituted with the IP\n"
               "\t\taddress of the machine trying to connect\n" );
        printf("Using configuration file %s\n", CFILE);
}

/**
 * Parse the command line.
 *
 * @param argc the argc argument to main()
 * @param argv the argv argument to main()
 **/
SERVER* cmdline(int argc, char *argv[]) {
        int i=0;
        int nonspecial=0;
        int c;
        struct option long_options[] = {
                {"read-only", no_argument, NULL, 'r'},
                {"multi-file", no_argument, NULL, 'm'},
                {"copy-on-write", no_argument, NULL, 'c'},
                {"authorize-file", required_argument, NULL, 'l'},
                {"idle-time", required_argument, NULL, 'a'},
                {"config-file", required_argument, NULL, 'C'},
                {0,0,0,0}
        };
        SERVER *serve;
        off_t es;
        size_t last;
        char suffix;

        if(argc==1) {
                return NULL;
        }
        serve=g_new0(SERVER, 1);
        serve->hunksize=OFFT_MAX;
        serve->authname = g_strdup(default_authname);
        while((c=getopt_long(argc, argv, "-a:C:cl:mr", long_options, &i))>=0) {
                switch (c) {
                case 1:
                        /* non-option argument */
                        switch(nonspecial++) {
                        case 0:
                                serve->port=strtol(optarg, NULL, 0);
                                break;
                        case 1:
                                serve->exportname = g_strdup(optarg);
                                if(serve->exportname[0] != '/') {
                                        fprintf(stderr, "E: The to be exported file needs to be an absolute filename!\n");
                                        exit(EXIT_FAILURE);
                                }
                                break;
                        case 2:
                                last=strlen(optarg)-1;
                                suffix=optarg[last];
                                if (suffix == 'k' || suffix == 'K' ||
                                    suffix == 'm' || suffix == 'M')
                                        optarg[last] = '\0';
                                es = (off_t)atol(optarg);
                                switch (suffix) {
                                        case 'm':
                                        case 'M':  es <<= 10;
                                        case 'k':
                                        case 'K':  es <<= 10;
                                        default :  break;
                                }
                                serve->expected_size = es;
                                break;
                        }
                        break;
                case 'r':
                        serve->flags |= F_READONLY;
                        break;
                case 'm':
                        serve->flags |= F_MULTIFILE;
                        serve->hunksize = 1*GIGA;
                        break;
                case 'c': 
                        serve->flags |=F_COPYONWRITE;
                        break;
                case 'C':
                        g_free(config_file_pos);
                        config_file_pos=g_strdup(optarg);
                        break;
                case 'l':
                        g_free(serve->authname);
                        serve->authname=g_strdup(optarg);
                        break;
                case 'a': 
                        serve->timeout=strtol(optarg, NULL, 0);
                        break;
                default:
                        usage();
                        exit(EXIT_FAILURE);
                        break;
                }
        }
        /* What's left: the port to export, the name of the to be exported
         * file, and, optionally, the size of the file, in that order. */
        if(nonspecial<2) {
                g_free(serve);
                serve=NULL;
        }
        return serve;
}

/**
 * Error codes for config file parsing
 **/
typedef enum {
        CFILE_NOTFOUND,         /**< The configuration file is not found */
        CFILE_MISSING_GENERIC,  /**< The (required) group "generic" is missing */
        CFILE_KEY_MISSING,      /**< A (required) key is missing */
        CFILE_VALUE_INVALID,    /**< A value is syntactically invalid */
        CFILE_PROGERR           /**< Programmer error */
} CFILE_ERRORS;

/**
 * Remove a SERVER from memory. Used from the hash table
 **/
void remove_server(gpointer s) {
        SERVER *server;

        server=(SERVER*)s;
        g_free(server->exportname);
        if(server->authname)
                g_free(server->authname);
        g_free(server);
}

/**
 * Parse the config file.
 *
 * @param f the name of the config file
 * @param e a GError. @see CFILE_ERRORS for what error values this function can
 *      return.
 * @return a GHashTable of SERVER* pointers, with the port number as the hash
 *      key. If the config file is empty or does not exist, returns an empty
 *      GHashTable; if the config file contains an error, returns NULL, and
 *      e is set appropriately
 **/
GArray* parse_cfile(gchar* f, GError** e) {
        const char* DEFAULT_ERROR = "Could not parse %s in group %s: %s";
        const char* MISSING_REQUIRED_ERROR = "Could not find required value %s in group %s: %s";
        SERVER s;
        PARAM p[] = {
                { "exportname", TRUE,   PARAM_STRING,   NULL, 0 },
                { "port",       TRUE,   PARAM_INT,      NULL, 0 },
                { "authfile",   FALSE,  PARAM_STRING,   NULL, 0 },
                { "timeout",    FALSE,  PARAM_INT,      NULL, 0 },
                { "filesize",   FALSE,  PARAM_INT,      NULL, 0 },
                { "readonly",   FALSE,  PARAM_BOOL,     NULL, F_READONLY },
                { "multifile",  FALSE,  PARAM_BOOL,     NULL, F_MULTIFILE },
                { "copyonwrite", FALSE, PARAM_BOOL,     NULL, F_COPYONWRITE },
        };
        const int p_size=8;
        GKeyFile *cfile;
        GError *err = NULL;
        const char *err_msg=NULL;
        GQuark errdomain;
        GArray *retval=NULL;
        gchar **groups;
        gboolean value;
        gint i,j;

        memset(&s, '\0', sizeof(SERVER));
        errdomain = g_quark_from_string("parse_cfile");
        cfile = g_key_file_new();
        retval = g_array_new(FALSE, TRUE, sizeof(SERVER));
        if(!g_key_file_load_from_file(cfile, f, G_KEY_FILE_KEEP_COMMENTS |
                        G_KEY_FILE_KEEP_TRANSLATIONS, &err)) {
                g_set_error(e, errdomain, CFILE_NOTFOUND, "Could not open config file.");
                g_key_file_free(cfile);
                return retval;
        }
        if(strcmp(g_key_file_get_start_group(cfile), "generic")) {
                g_set_error(e, errdomain, CFILE_MISSING_GENERIC, "Config file does not contain the [generic] group!");
                g_key_file_free(cfile);
                return NULL;
        }
        groups = g_key_file_get_groups(cfile, NULL);
        for(i=1;groups[i];i++) {
                p[0].target=&(s.exportname);
                p[1].target=&(s.port);
                p[2].target=&(s.authname);
                p[3].target=&(s.timeout);
                p[4].target=&(s.expected_size);
                p[5].target=p[6].target=p[7].target=&(s.flags);
                for(j=0;j<p_size;j++) {
                        g_assert(p[j].target != NULL);
                        g_assert(p[j].ptype==PARAM_INT||p[j].ptype==PARAM_STRING||p[j].ptype==PARAM_BOOL);
                        switch(p[j].ptype) {
                                case PARAM_INT:
                                        *((gint*)p[j].target) =
                                                g_key_file_get_integer(cfile,
                                                                groups[i],
                                                                p[j].paramname,
                                                                &err);
                                        break;
                                case PARAM_STRING:
                                        *((gchar**)p[j].target) =
                                                g_key_file_get_string(cfile,
                                                                groups[i],
                                                                p[j].paramname,
                                                                &err);
                                        break;
                                case PARAM_BOOL:
                                        value = g_key_file_get_boolean(cfile,
                                                        groups[i],
                                                        p[j].paramname, &err);
                                        if(!err && value) {
                                                *((gint*)p[j].target) |= p[j].flagval;
                                        }
                                        break;
                        }
                        if(err) {
                                if(err->code == G_KEY_FILE_ERROR_KEY_NOT_FOUND) {
                                        if(!p[j].required) {
                                                /* Ignore not-found error for optional values */
                                                g_clear_error(&err);
                                                continue;
                                        } else {
                                                err_msg = MISSING_REQUIRED_ERROR;
                                        }
                                } else {
                                        err_msg = DEFAULT_ERROR;
                                }
                                g_set_error(e, errdomain, CFILE_VALUE_INVALID, err_msg, p[j].paramname, groups[i], err->message);
                                g_array_free(retval, TRUE);
                                g_error_free(err);
                                g_key_file_free(cfile);
                                return NULL;
                        }
                }
                if(s.flags & F_MULTIFILE)
                        s.hunksize = 1*GIGA;
                else
                        s.hunksize = OFFT_MAX;
                g_array_append_val(retval, s);
        }
        return retval;
}

/**
 * Signal handler for SIGCHLD
 * @param s the signal we're handling (must be SIGCHLD, or something
 * is severely wrong)
 **/
void sigchld_handler(int s) {
        int status;
        int* i;
        pid_t pid;

        while((pid=waitpid(-1, &status, WNOHANG)) > 0) {
                if(WIFEXITED(&status)) {
                        msg3(LOG_INFO, "Child exited with %d", WEXITSTATUS(status));
                }
                i=g_hash_table_lookup(children, &pid);
                if(!i) {
                        msg3(LOG_INFO, "SIGCHLD received for an unknown child with PID %ld", (long)pid);
                } else {
                        DEBUG2("Removing %d from the list of children", pid);
                        g_hash_table_remove(children, &pid);
                }
        }
}

/**
 * Kill a child. Called from sigterm_handler::g_hash_table_foreach.
 *
 * @param key the key
 * @param value the value corresponding to the above key
 * @param user_data a pointer which we always set to 1, so that we know what
 * will happen next.
 **/
void killchild(gpointer key, gpointer value, gpointer user_data) {
        pid_t *pid=value;
        int *parent=user_data;

        kill(*pid, SIGTERM);
        *parent=1;
}

/**
 * Handle SIGTERM and dispatch it to our children
 * @param s the signal we're handling (must be SIGTERM, or something
 * is severely wrong).
 **/
void sigterm_handler(int s) {
        int parent=0;

        g_hash_table_foreach(children, killchild, &parent);

        if(parent) {
                unlink(pidfname);
        }

        exit(0);
}

/**
 * Detect the size of a file.
 *
 * @param export An open filedescriptor
 * @return the size of the file, or OFFT_MAX if detection was
 * impossible.
 **/
off_t size_autodetect(int export) {
        off_t es;
        u32 es32;
        struct stat stat_buf;
        int error;

#ifdef HAVE_SYS_MOUNT_H
#ifdef HAVE_SYS_IOCTL_H
#ifdef BLKGETSIZE
        DEBUG("looking for export size with ioctl BLKGETSIZE\n");
        if (!ioctl(export, BLKGETSIZE, &es32) && es32) {
                es = (off_t)es32 * (off_t)512;
                return es;
        }
#endif /* BLKGETSIZE */
#endif /* HAVE_SYS_IOCTL_H */
#endif /* HAVE_SYS_MOUNT_H */

        DEBUG("looking for export size with fstat\n");
        stat_buf.st_size = 0;
        error = fstat(export, &stat_buf);
        if (!error) {
                if(stat_buf.st_size > 0)
                        return (off_t)stat_buf.st_size;
        } else {
                err("fstat failed: %m");
        }

        DEBUG("looking for export size with lseek SEEK_END\n");
        es = lseek(export, (off_t)0, SEEK_END);
        if (es > ((off_t)0)) {
                return es;
        } else {
                DEBUG2("lseek failed: %d", errno==EBADF?1:(errno==ESPIPE?2:(errno==EINVAL?3:4)));
        }

        err("Could not find size of exported block device: %m");
        return OFFT_MAX;
}

/**
 * seek to a position in a file, with error handling.
 * @param handle a filedescriptor
 * @param a position to seek to
 * @todo get rid of this; lastpoint is a global variable right now, but it
 * shouldn't be. If we pass it on as a parameter, that makes things a *lot*
 * easier.
 **/
void myseek(int handle,off_t a) {
        if (lseek(handle, a, SEEK_SET) < 0) {
                err("Can not seek locally!\n");
        }
}

/**
 * Write an amount of bytes at a given offset to the right file. This
 * abstracts the write-side of the multiple file option.
 *
 * @param a The offset where the write should start
 * @param buf The buffer to write from
 * @param len The length of buf
 * @param client The client we're serving for
 * @return The number of bytes actually written, or -1 in case of an error
 **/
int rawexpwrite(off_t a, char *buf, size_t len, CLIENT *client) {
        ssize_t res;

        myseek(g_array_index(client->export, int, (int)(a/client->server->hunksize)), a%client->server->hunksize);
        ;
        res = write(g_array_index(client->export, int, (int)((off_t)a/(off_t)(client->server->hunksize))), buf, len);
        return (res < 0 || (size_t)res != len);
}

/**
 * Read an amount of bytes at a given offset from the right file. This
 * abstracts the read-side of the multiple files option.
 *
 * @param a The offset where the read should start
 * @param buf A buffer to read into
 * @param len The size of buf
 * @param client The client we're serving for
 * @return The number of bytes actually read, or -1 in case of an
 * error.
 **/
int rawexpread(off_t a, char *buf, size_t len, CLIENT *client) {
        ssize_t res;

        myseek(g_array_index(client->export,int,(int)a/client->server->hunksize),
                        a%client->server->hunksize);
        res = read(g_array_index(client->export,int,(int)a/client->server->hunksize), buf, len);
        return (res < 0 || (size_t)res != len);
}

/**
 * Read an amount of bytes at a given offset from the right file. This
 * abstracts the read-side of the copyonwrite stuff, and calls
 * rawexpread() with the right parameters to do the actual work.
 * @param a The offset where the read should start
 * @param buf A buffer to read into
 * @param len The size of buf
 * @param client The client we're going to read for
 * @return The number of bytes actually read, or -1 in case of an error
 **/
int expread(off_t a, char *buf, size_t len, CLIENT *client) {
        off_t rdlen, offset;
        off_t mapcnt, mapl, maph, pagestart;

        if (!(client->server->flags & F_COPYONWRITE))
                return rawexpread(a, buf, len, client);
        DEBUG3("Asked to read %d bytes at %Lu.\n", len, (unsigned long long)a);

        mapl=a/DIFFPAGESIZE; maph=(a+len-1)/DIFFPAGESIZE;

        for (mapcnt=mapl;mapcnt<=maph;mapcnt++) {
                pagestart=mapcnt*DIFFPAGESIZE;
                offset=a-pagestart;
                rdlen=(0<DIFFPAGESIZE-offset && len<(size_t)(DIFFPAGESIZE-offset)) ?
                        len : (size_t)DIFFPAGESIZE-offset;
                if (client->difmap[mapcnt]!=(u32)(-1)) { /* the block is already there */
                        DEBUG3("Page %Lu is at %lu\n", (unsigned long long)mapcnt,
                               (unsigned long)(client->difmap[mapcnt]));
                        myseek(client->difffile, client->difmap[mapcnt]*DIFFPAGESIZE+offset);
                        if (read(client->difffile, buf, rdlen) != rdlen) return -1;
                } else { /* the block is not there */
                        DEBUG2("Page %Lu is not here, we read the original one\n",
                               (unsigned long long)mapcnt);
                        if(rawexpread(a, buf, rdlen, client)) return -1;
                }
                len-=rdlen; a+=rdlen; buf+=rdlen;
        }
        return 0;
}

/**
 * Write an amount of bytes at a given offset to the right file. This
 * abstracts the write-side of the copyonwrite option, and calls
 * rawexpwrite() with the right parameters to do the actual work.
 *
 * @param a The offset where the write should start
 * @param buf The buffer to write from
 * @param len The length of buf
 * @param client The client we're going to write for.
 * @return The number of bytes actually written, or -1 in case of an error
 **/
int expwrite(off_t a, char *buf, size_t len, CLIENT *client) {
        char pagebuf[DIFFPAGESIZE];
        off_t mapcnt,mapl,maph;
        off_t wrlen,rdlen; 
        off_t pagestart;
        off_t offset;

        if (!(client->server->flags & F_COPYONWRITE))
                return(rawexpwrite(a,buf,len, client)); 
        DEBUG3("Asked to write %d bytes at %Lu.\n", len, (unsigned long long)a);

        mapl=a/DIFFPAGESIZE ; maph=(a+len-1)/DIFFPAGESIZE ;

        for (mapcnt=mapl;mapcnt<=maph;mapcnt++) {
                pagestart=mapcnt*DIFFPAGESIZE ;
                offset=a-pagestart ;
                wrlen=(0<DIFFPAGESIZE-offset && len<(size_t)(DIFFPAGESIZE-offset)) ?
                        len : (size_t)DIFFPAGESIZE-offset;

                if (client->difmap[mapcnt]!=(u32)(-1)) { /* the block is already there */
                        DEBUG3("Page %Lu is at %lu\n", (unsigned long long)mapcnt,
                               (unsigned long)(client->difmap[mapcnt])) ;
                        myseek(client->difffile,
                                        client->difmap[mapcnt]*DIFFPAGESIZE+offset);
                        if (write(client->difffile, buf, wrlen) != wrlen) return -1 ;
                } else { /* the block is not there */
                        myseek(client->difffile,client->difffilelen*DIFFPAGESIZE) ;
                        client->difmap[mapcnt]=client->difffilelen++ ;
                        DEBUG3("Page %Lu is not here, we put it at %lu\n",
                               (unsigned long long)mapcnt,
                               (unsigned long)(client->difmap[mapcnt]));
                        rdlen=DIFFPAGESIZE ;
                        if (rdlen+pagestart%(client->server->hunksize) >
                                        (client->server->hunksize)) 
                                rdlen=client->server->hunksize -
                                        (pagestart%client->server->hunksize);
                        if (rawexpread(pagestart, pagebuf, rdlen, client))
                                return -1;
                        memcpy(pagebuf+offset,buf,wrlen) ;
                        if (write(client->difffile, pagebuf, DIFFPAGESIZE) !=
                                        DIFFPAGESIZE)
                                return -1;
                }                                                   
                len-=wrlen ; a+=wrlen ; buf+=wrlen ;
        }
        return 0;
}

/**
 * Do the initial negotiation.
 *
 * @param client The client we're negotiating with.
 **/
void negotiate(CLIENT *client) {
        char zeros[300];
        u64 size_host;

        memset(zeros, 0, 290);
        if (write(client->net, INIT_PASSWD, 8) < 0)
                err("Negotiation failed: %m");
        cliserv_magic = htonll(cliserv_magic);
        if (write(client->net, &cliserv_magic, sizeof(cliserv_magic)) < 0)
                err("Negotiation failed: %m");
        size_host = htonll((u64)(client->exportsize));
        if (write(client->net, &size_host, 8) < 0)
                err("Negotiation failed: %m");
        if (write(client->net, zeros, 128) < 0)
                err("Negotiation failed: %m");
}

/** sending macro. */
#define SEND(net,reply) writeit( net, &reply, sizeof( reply ));
/** error macro. */
#define ERROR(client,reply) { reply.error = htonl(-1); SEND(client->net,reply); reply.error = 0; }
/**
 * Serve a file to a single client.
 *
 * @todo This beast needs to be split up in many tiny little manageable
 * pieces. Preferably with a chainsaw.
 *
 * @param client The client we're going to serve to.
 * @return never
 **/
int mainloop(CLIENT *client) {
        struct nbd_request request;
        struct nbd_reply reply;
        gboolean go_on=TRUE;
#ifdef DODBG
        int i = 0;
#endif
        negotiate(client);
        DEBUG("Entering request loop!\n");
        reply.magic = htonl(NBD_REPLY_MAGIC);
        reply.error = 0;
        while (go_on) {
                char buf[BUFSIZE];
                size_t len;
#ifdef DODBG
                i++;
                printf("%d: ", i);
#endif
                if (client->server->timeout) 
                        alarm(client->server->timeout);
                readit(client->net, &request, sizeof(request));
                request.from = ntohll(request.from);
                request.type = ntohl(request.type);

                if (request.type==NBD_CMD_DISC) {
                        msg2(LOG_INFO, "Disconnect request received.");
                        if (client->difmap) g_free(client->difmap) ;
                        if (client->difffile>=0) { 
                                close(client->difffile);
                                unlink(client->difffilename);
                                free(client->difffilename);
                        }
                        go_on=FALSE;
                        continue;
                }

                len = ntohl(request.len);

                if (request.magic != htonl(NBD_REQUEST_MAGIC))
                        err("Not enough magic.");
                if (len > BUFSIZE + sizeof(struct nbd_reply))
                        err("Request too big!");
#ifdef DODBG
                printf("%s from %Lu (%Lu) len %d, ", request.type ? "WRITE" :
                                "READ", (unsigned long long)request.from,
                                (unsigned long long)request.from / 512, len);
#endif
                memcpy(reply.handle, request.handle, sizeof(reply.handle));
                if ((request.from + len) > (OFFT_MAX)) {
                        DEBUG("[Number too large!]");
                        ERROR(client, reply);
                        continue;
                }

                if (((ssize_t)((off_t)request.from + len) > client->exportsize) ||
                    ((client->server->flags & F_READONLY) && request.type)) {
                        DEBUG("[RANGE!]");
                        ERROR(client, reply);
                        continue;
                }

                if (request.type==NBD_CMD_WRITE) {
                        DEBUG("wr: net->buf, ");
                        readit(client->net, buf, len);
                        DEBUG("buf->exp, ");
                        if ((client->server->flags & F_AUTOREADONLY) ||
                                        expwrite(request.from, buf, len,
                                                client)) {
                                DEBUG("Write failed: %m" );
                                ERROR(client, reply);
                                continue;
                        }
                        SEND(client->net, reply);
                        DEBUG("OK!\n");
                        continue;
                }
                /* READ */

                DEBUG("exp->buf, ");
                if (expread(request.from, buf + sizeof(struct nbd_reply), len, client)) {
                        DEBUG("Read failed: %m");
                        ERROR(client, reply);
                        continue;
                }

                DEBUG("buf->net, ");
                memcpy(buf, &reply, sizeof(struct nbd_reply));
                writeit(client->net, buf, len + sizeof(struct nbd_reply));
                DEBUG("OK!\n");
        }
        return 0;
}

/**
 * Set up client export array, which is an array of file handles.
 * Also, split a single exportfile into multiple ones, if that was asked.
 * @return 0 on success, -1 on failure
 * @param client information on the client which we want to split
 **/
int setupexport(CLIENT* client) {
        int i;
        int multifile = (client->server->flags & F_MULTIFILE);

        client->export = g_array_new(TRUE, TRUE, sizeof(int));

        /* If multifile, open as many files as we can.
         * For non-multifile, open exactly one file.
         * (Either way, we must be able to open at least one file.) */
        for(i=0; ; i++) {
                int fhandle;
                gchar *tmpname;
                mode_t mode = (client->server->flags & F_READONLY) ? O_RDONLY : O_RDWR;

                if(multifile) {
                        tmpname=g_strdup_printf("%s.%d", client->exportname, i);
                } else {
                        tmpname=g_strdup(client->exportname);
                }
                DEBUG2( "Opening %s\n", tmpname );
                fhandle = open(tmpname, mode);
                if(fhandle == -1 && mode == O_RDWR) {
                        /* Try again because maybe media was read-only */
                        fhandle = open(tmpname, O_RDONLY);
                        if(fhandle != -1) {
                                client->server->flags |= F_AUTOREADONLY;
                                client->server->flags |= F_READONLY;
                        }
                }
                if(fhandle == -1) {
                        if(multifile && i*(client->server->hunksize) >= client->exportsize)
                                break;
                        err("Could not open exported file: %m");
                }
                g_array_insert_val(client->export, i, fhandle);
                g_free(tmpname);

                if(!multifile)
                        break;
        }
        return 0;
}

int copyonwrite_prepare(CLIENT* client) {
        off_t i;
        if ((client->difffilename = malloc(1024))==NULL)
                err("Failed to allocate string for diff file name");
        snprintf(client->difffilename, 1024, "%s-%s-%d.diff",client->exportname,client->clientname,
                (int)getpid()) ;
        client->difffilename[1023]='\0';
        msg3(LOG_INFO,"About to create map and diff file %s",client->difffilename) ;
        client->difffile=open(client->difffilename,O_RDWR | O_CREAT | O_TRUNC,0600) ;
        if (client->difffile<0) err("Could not create diff file (%m)") ;
        if ((client->difmap=calloc(client->exportsize/DIFFPAGESIZE,sizeof(u32)))==NULL)
                err("Could not allocate memory") ;
        for (i=0;i<client->exportsize/DIFFPAGESIZE;i++) client->difmap[i]=(u32)-1 ;

        return 0;
}

/**
 * Serve a connection. 
 *
 * @todo allow for multithreading, perhaps use libevent. Not just yet, though;
 * follow the road map.
 *
 * @param client a connected client
 **/
void serveconnection(CLIENT *client) {
        setupexport(client);

        /* Sanity check. There must be at least one file. */
        if(client->export->len == 0)
                err("No file(s) to export\n");

        if (!client->server->expected_size) {
                client->exportsize = size_autodetect(g_array_index(client->export,int,0));
        } else {
                /* Perhaps we should check first. Not now. */
                client->exportsize = client->server->expected_size;
        }
        if (client->exportsize > OFFT_MAX) {
                /* uhm, well... In a parallel universe, this *might* be
                 * possible... */
                err("Size of exported file is too big\n");
        }
        else {
                msg3(LOG_INFO, "size of exported file/device is %Lu", (unsigned long long)client->exportsize);
        }

        if (client->server->flags & F_COPYONWRITE) {
                copyonwrite_prepare(client);
        }

        setmysockopt(client->net);

        mainloop(client);
}

/**
 * Find the name of the file we have to serve. This will use g_strdup_printf
 * to put the IP address of the client inside a filename containing
 * "%s". That name is then written to client->exportname.
 *
 * @param net A socket connected to an nbd client
 * @param client information about the client. The IP address in human-readable
 * format will be written to a new char* buffer, the address of which will be
 * stored in client->clientname.
 **/
void set_peername(int net, CLIENT *client) {
        struct sockaddr_in addrin;
        int addrinlen = sizeof( addrin );
        char *peername ;

        if (getpeername(net, (struct sockaddr *) &addrin, (socklen_t *)&addrinlen) < 0)
                err("getsockname failed: %m");
        peername = inet_ntoa(addrin.sin_addr);
        client->exportname=g_strdup_printf(client->server->exportname, peername);

        msg4(LOG_INFO, "connect from %s, assigned file is %s", 
             peername, client->exportname);
        client->clientname=g_strdup(peername);
}

/**
 * Destroy a pid_t*
 * @param data a pointer to pid_t which should be freed
 **/
void destroy_pid_t(gpointer data) {
        g_free(data);
}

/**
 * Go daemon (unless we specified at compile time that we didn't want this)
 * @param serve the first server of our configuration. If its port is zero,
 *      then do not daemonize, because we're doing inetd then. This parameter
 *      is only used to create a PID file of the form
 *      /var/run/nbd-server.&lt;port&gt;.pid; it's not modified in any way.
 **/
#if !defined(NODAEMON) && !defined(NOFORK)
void daemonize(SERVER* serve) {
        FILE*pidf;

        if(daemon(0,0)<0) {
                err("daemon");
        }
        if(serve) {
                snprintf(pidfname, sizeof(char)*255, "/var/run/nbd-server.%d.pid", serve->port);
        } else {
                strncpy(pidfname, "/var/run/nbd-server.pid", sizeof(char)*255);
        }
        pidf=fopen(pidfname, "w");
        if(pidf) {
                fprintf(pidf,"%d\n", (int)getpid());
                fclose(pidf);
        } else {
                perror("fopen");
                fprintf(stderr, "Not fatal; continuing");
        }
}
#else
#define daemonize(serve)
#endif /* !defined(NODAEMON) && !defined(NOFORK) */

/**
 * Connect a server's socket.
 *
 * @param serve the server we want to connect.
 **/
void setup_serve(SERVER *serve) {
        struct sockaddr_in addrin;
        struct sigaction sa;
        int addrinlen = sizeof(addrin);
        int sock_flags;
#ifndef sun
        int yes=1;
#else
        char yes='1';
#endif /* sun */
        if ((serve->socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
                err("socket: %m");

        /* lose the pesky "Address already in use" error message */
        if (setsockopt(serve->socket,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
                err("setsockopt SO_REUSEADDR");
        }
        if (setsockopt(serve->socket,SOL_SOCKET,SO_KEEPALIVE,&yes,sizeof(int)) == -1) {
                err("setsockopt SO_KEEPALIVE");
        }

        /* make the listening socket non-blocking */
        if ((sock_flags = fcntl(serve->socket, F_GETFL, 0)) == -1) {
                err("fcntl F_GETFL");
        }
        if (fcntl(serve->socket, F_SETFL, sock_flags | O_NONBLOCK) == -1) {
                err("fcntl F_SETFL O_NONBLOCK");
        }

        DEBUG("Waiting for connections... bind, ");
        addrin.sin_family = AF_INET;
        addrin.sin_port = htons(serve->port);
        addrin.sin_addr.s_addr = 0;
        if (bind(serve->socket, (struct sockaddr *) &addrin, addrinlen) < 0)
                err("bind: %m");
        DEBUG("listen, ");
        if (listen(serve->socket, 1) < 0)
                err("listen: %m");
        sa.sa_handler = sigchld_handler;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        if(sigaction(SIGCHLD, &sa, NULL) == -1)
                err("sigaction: %m");
        sa.sa_handler = sigterm_handler;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        if(sigaction(SIGTERM, &sa, NULL) == -1)
                err("sigaction: %m");
        children=g_hash_table_new_full(g_int_hash, g_int_equal, NULL, destroy_pid_t);
}

/**
 * Connect our servers.
 **/
void setup_servers(GArray* servers) {
        int i;

        for(i=0;i<servers->len;i++) {
                setup_serve(&(g_array_index(servers, SERVER, i)));
        }
}

/**
 * Loop through the available servers, and serve them.
 **/
int serveloop(GArray* servers) {
        struct sockaddr_in addrin;
        socklen_t addrinlen=sizeof(addrin);
        SERVER *serve;
        int i;
        int max;
        int sock;
        fd_set mset;
        fd_set rset;
        struct timeval tv;

        /* 
         * Set up the master fd_set. The set of descriptors we need
         * to select() for never changes anyway and it buys us a *lot*
         * of time to only build this once. However, if we ever choose
         * to not fork() for clients anymore, we may have to revisit
         * this.
         */
        max=0;
        FD_ZERO(&mset);
        for(i=0;i<servers->len;i++) {
                sock=(g_array_index(servers, SERVER, i)).socket;
                FD_SET(sock, &mset);
                max=sock>max?sock:max;
        }
        for(;;) {
                CLIENT *client;
                int net;
                pid_t *pid;

                memcpy(&rset, &mset, sizeof(fd_set));
                tv.tv_sec=0;
                tv.tv_usec=500;
                if(select(max+1, &rset, NULL, NULL, &tv)>0) {
                        DEBUG("accept, ");
                        for(i=0;i<servers->len;i++) {
                                serve=&(g_array_index(servers, SERVER, i));
                                if(FD_ISSET(serve->socket, &rset)) {
                                        if ((net=accept(serve->socket, (struct sockaddr *) &addrin, &addrinlen)) < 0)
                                                err("accept: %m");

                                        client = g_malloc(sizeof(CLIENT));
                                        client->server=serve;
                                        client->exportsize=OFFT_MAX;
                                        client->net=net;
                                        set_peername(net, client);
                                        if (!authorized_client(client)) {
                                                msg2(LOG_INFO,"Unauthorized client") ;
                                                close(net);
                                                continue;
                                        }
                                        msg2(LOG_INFO,"Authorized client") ;
                                        pid=g_malloc(sizeof(pid_t));
#ifndef NOFORK
                                        if ((*pid=fork())<0) {
                                                msg3(LOG_INFO,"Could not fork (%s)",strerror(errno)) ;
                                                close(net);
                                                continue;
                                        }
                                        if (*pid>0) { /* parent */
                                                close(net);
                                                g_hash_table_insert(children, pid, pid);
                                                continue;
                                        }
                                        /* child */
                                        g_hash_table_destroy(children);
                                        for(i=0;i<servers->len,serve=(g_array_index(servers, SERVER*, i));i++) {
                                                close(serve->socket);
                                        }
                                        /* FALSE does not free the
                                        actual data. This is required,
                                        because the client has a
                                        direct reference into that
                                        data, and otherwise we get a
                                        segfault... */
                                        g_array_free(servers, FALSE);
#endif // NOFORK
                                        msg2(LOG_INFO,"Starting to serve");
                                        serveconnection(client);
                                }
                        }
                }
        }
}

/**
 * Main entry point...
 **/
int main(int argc, char *argv[]) {
        SERVER *serve;
        GArray *servers;
        GError *err=NULL;

        if (sizeof( struct nbd_request )!=28) {
                fprintf(stderr,"Bad size of structure. Alignment problems?\n");
                exit(-1) ;
        }

        logging();
        config_file_pos = g_strdup(CFILE);
        serve=cmdline(argc, argv);
        servers = parse_cfile(config_file_pos, &err);
        if(!servers || !servers->len) {
                g_warning("Could not parse config file: %s", err->message);
        }
        if(serve) {
                g_array_append_val(servers, *serve);
        }

/* We don't support this at this time */
#if 0
        if (!(serve->port)) {
                CLIENT *client;
#ifndef ISSERVER
                /* You really should define ISSERVER if you're going to use
                 * inetd mode, but if you don't, closing stdout and stderr
                 * (which inetd had connected to the client socket) will let it
                 * work. */
                close(1);
                close(2);
                open("/dev/null", O_WRONLY);
                open("/dev/null", O_WRONLY);
#endif
                client=g_malloc(sizeof(CLIENT));
                client->server=serve;
                client->net=0;
                client->exportsize=OFFT_MAX;
                set_peername(0,client);
                serveconnection(client);
                return 0;
        }
#endif
        if((!serve) && (!servers||!servers->len)) {
                g_message("Nothing to do! Bye!");
                exit(EXIT_FAILURE);
        }
        daemonize(serve);
        setup_servers(servers);
        serveloop(servers);
        return 0 ;
}