r82: Stop using global variables.

[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 "config.h"
#include "lfs.h"

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#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"

/** how much space for child PIDs we have by default. Dynamically
   allocated, and will be realloc()ed if out of space, so this should
   probably be fair for most situations. */
#define DEFAULT_CHILD_ARRAY 256

/** Logging macros, now nothing goes to syslog unless you say ISSERVER */
#ifdef ISSERVER
#define msg2(a,b) syslog(a,"%s", b)
#define msg3(a,b,c) syslog(a,"%s %s", b,c)
#define msg4(a,b,c,d) syslog(a,"%s %s %s", b,c,d)
#else
#define msg2(a,b) g_message(a,b)
#define msg3(a,b,c) g_message(a,b,c)
#define msg4(a,b,c,d) g_message(a,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 starting to get ugly. If someone knows a better way to find
 * the maximum value of a signed type *without* relying on overflow
 * (doing so breaks on 64bit architectures), that would be nice.
 *
 * Actually, do we need this at all? Can't we just say '0 is autodetect', and
 * live with it? Or better yet, use an extra flag, or so?
 */
#define OFFT_MAX (((((off_t)1)<<((sizeof(off_t)-1)*8))-1)<<7)+127
#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 */
#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 */
//char difffilename[1024]; /**< filename of the copy-on-write file. Doesn't belong here! */
//unsigned int timeout = 0; /**< disconnect timeout */
//int autoreadonly = 0; /**< 1 = switch to readonly if opening readwrite isn't
//                      possible */
//char *auth_file="nbd_server.allow"; /**< authorization file */
//char exportname2[1024]; /**< File I'm exporting, with virtualhost resolved */
//off_t lastpoint = (off_t)-1;  /**< keep track of where we are in the file, to
//                                avoid an lseek if possible */
//char pagebuf[DIFFPAGESIZE];   /**< when doing copyonwrite, this is
//                                used as a temporary buffer to store
//                                the exported block in. @todo this is
//                                a great example of namespace
//                                pollution. Throw it out. */
//unsigned int port;            /**< Port I'm listening at */
//char *exportname;             /**< File I'm exporting */
//off_t exportsize = OFFT_MAX;  /**< length of file I'm exporting */
//off_t hunksize = OFFT_MAX;      /**< size of each exported file in case of -m */
//int flags = 0;                        /**< flags associated with this exported file */
//int export[1024];/**< array of filedescriptors of exported files; only first is
//                 used unless -m option is activated */ 
//int difffile=-1; /**< filedescriptor for copyonwrite file */
//u32 difffilelen=0 ; /**< number of pages in difffile */
//u32 *difmap=NULL ; /**< Determine whether a block is in the original file
//                   (difmap[block]==-1) or in the copyonwrite file (in which
//                   case it contains the offset where it is to be found in the
//                   copyonwrite file). @todo the kernel knows about sparse
//                   files, we should use those instead. Should also be off_t
//                   instead of u32; copyonwrite is probably broken wrt LFS */
char clientname[256] ;
int child_arraysize=DEFAULT_CHILD_ARRAY; /**< number of available slots for
                                           child array */
pid_t *children; /**< child array */
char pidfname[256]; /**< name of our PID file */

/**
 * Variables associated with a server.
 **/
typedef struct {
        char* 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) */
} 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 */
        int export[1024];    /**< array of filedescriptors of exported files;
                               only the first is actually used unless we're
                               doing the multiple file option */
        int lastpoint;       /**< For keeping track of where we are in a file.
                               This code is BUGGY currently, at least in
                               combination with 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
                               nbd_server_opts::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;

/**
 * Check whether a client is allowed to connect. Works with an authorization
 * file which contains one line per machine, no wildcards.
 *
 * @param name IP address of client trying to connect (in human-readable form)
 * @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] [-r] [-m] [-c] [-a timeout_sec]\n"
               "        -r read only\n"
               "        -m multiple file\n"
               "        -c copy on write\n"
               "        -l file with list of hosts that are allowed to connect.\n"
               "        -a maximum idle seconds, terminates when idle time exceeded\n"
               "        if port is set to 0, stdin is used (for running from inetd)\n"
               "        if file_to_export contains '%%s', it is substituted with IP\n"
               "                address of machine trying to connect\n" );
}

/**
 * Parse the command line.
 *
 * @todo getopt() is a great thing, and easy to use. Also, we want to
 * create a configuration file which nbd-server will read. Maybe do (as in,
 * parse) that here.
 *
 * @param argc the argc argument to main()
 * @param argv the argv argument to main()
 **/
SERVER* cmdline(int argc, char *argv[]) {
        int i;
        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'},
                {0,0,0,0}
        };
        SERVER *serve;

        serve=g_malloc(sizeof(SERVER));
        while((c=getopt_long(argc, argv, "a:cl:mr", long_options, &i))>=0) {
                switch (c) {
                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 'l':
                        serve->authname=optarg;
                        break;
                case 'a': 
                        serve->timeout=strtol(optarg, NULL, 0);
                        break;
                default:
                        usage();
                        exit(0);
                        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(++i>argc) {
                usage();
                exit(0);
        } 
        serve->port=strtol(argv[i], NULL, 0);
        if(++i>argc) {
                usage();
                exit(0);
        }
        serve->exportname = argv[i];
        if(++i<=argc) {
                off_t es;
                size_t last = strlen(argv[i])-1;
                char suffix = argv[i][last];
                if (suffix == 'k' || suffix == 'K' ||
                    suffix == 'm' || suffix == 'M')
                        argv[i][last] = '\0';
                es = (off_t)atol(argv[i]);
                switch (suffix) {
                        case 'm':
                        case 'M':  es <<= 10;
                        case 'k':
                        case 'K':  es <<= 10;
                        default :  break;
                }
                serve->expected_size = es;
        }
        return serve;
}

/**
 * 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=NULL;
        int i;
        char buf[80];
        pid_t pid;

        while((pid=wait(status)) > 0) {
                if(WIFEXITED(status)) {
                        memset(buf,'\0', 80);
                        snprintf(buf, 79, "%d", WEXITSTATUS(status));
                        msg3(LOG_INFO, "Child exited with ", buf);
                }
                for(i=0;children[i]!=pid&&i<child_arraysize;i++);
                if(i>=child_arraysize) {
                        memset(buf, '\0', 80);
                        snprintf(buf, 79, "%ld", (long)pid);
                        msg3(LOG_INFO, "SIGCHLD received for an unknown child with PID ", buf);
                } else {
                        children[i]=(pid_t)0;
                        DEBUG2("Removing %d from the list of children", pid);
                }
        }
}

/**
 * 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 i;
        int parent=0;

        for(i=0;i<child_arraysize;i++) {
                if(children[i]) {
                        kill(children[i], s);
                        parent=1;
                }
        }

        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 && 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, unless we're already there.
 * @param handle a filedescriptor
 * @param a position to seek to
 * @param client the client we're working for
 **/
void maybeseek(int handle, off_t a, CLIENT* client) {
        if (a < 0 || a > client->exportsize) {
                err("Can not happen\n");
        }
        if (client->lastpoint != a) {
                if (lseek(handle, a, SEEK_SET) < 0) {
                        err("Can not seek locally!\n");
                }
                client->lastpoint = a;
        } else {
                DEBUG("S");
        }
}

/**
 * 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
 * @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;

        maybeseek(client->export[a/client->server->hunksize],
                        a%client->server->hunksize, client);
        res = write(client->export[a/client->server->hunksize], buf, len);
        return (res < 0 || (size_t)res != len);
}

/**
 * seek to a position in a file, no matter what. Used when using maybeseek is a
 * bad idea (for instance, because we're reading the copyonwrite file instead
 * of the exported file).
 * @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");
        }
}

/**
 * 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
 * @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;

        maybeseek(client->export[a/client->server->hunksize],
                        a%client->server->hunksize, client);
        res = read(client->export[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
 * @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)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);
                        return rawexpread(a, buf, rdlen, client);
                }
                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
 * @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)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)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 net A socket to do the negotiation over
 **/
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; client->lastpoint = -1; }
/**
 * 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 net A network socket, connected to an nbd client
 * @return never
 **/
int mainloop(CLIENT *client)
{
        struct nbd_request request;
        struct nbd_reply reply;
#ifdef DODBG
        int i = 0;
#endif
        negotiate(client);
        DEBUG("Entering request loop!\n");
        reply.magic = htonl(NBD_REPLY_MAGIC);
        reply.error = 0;
        while (1) {
                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) { /* Disconnect request */
                  if (client->difmap) free(client->difmap) ;
                  if (client->difffile>=0) { 
                     close(client->difffile) ; unlink(client->difffilename) ; }
                  err("Disconnect request received.") ;
                }

                len = ntohl(request.len);

                if (request.magic != htonl(NBD_REQUEST_MAGIC))
                        err("Not enough magic.");
                if (len > BUFSIZE)
                        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==1) {  /* 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;
                        }
                        client->lastpoint += len;
                        SEND(client->net, reply);
                        DEBUG("OK!\n");
                        continue;
                }
                /* READ */

                DEBUG("exp->buf, ");
                if (expread(request.from, buf + sizeof(struct nbd_reply), len, client)) {
                        client->lastpoint = -1;
                        DEBUG("Read failed: %m");
                        ERROR(client, reply);
                        continue;
                }
                client->lastpoint += len;

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

/**
 * 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 splitexport(CLIENT* client) {
        off_t i;

        for (i=0; i<client->exportsize; i+=client->server->hunksize) {
                char tmpname[1024];

                if(client->server->flags & F_MULTIFILE) {
                        snprintf(tmpname, 1024, "%s.%d", client->exportname,
                                        (int)(i/client->server->hunksize));
                } else {
                        strncpy(client->exportname, client->server->exportname, 1024);
                }
                tmpname[1023]='\0';
                DEBUG2( "Opening %s\n", tmpname );
                if ((client->export[ i/ client->server->hunksize ] =
                                        open(tmpname, (client->server->flags &
                                                        F_READONLY) ? O_RDONLY
                                                : O_RDWR)) == -1) {
                        /* Read WRITE ACCESS was requested by media is only read only */
                        client->server->flags |= F_AUTOREADONLY;
                        client->server->flags |= F_READONLY;
                        if ((client->export[i/client->server->hunksize] =
                                                open(tmpname, O_RDONLY)) == -1) 
                                err("Could not open exported file: %m");
                }
        }

        if (client->server->flags & F_COPYONWRITE) {
                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.
 *
 * @param net A network socket connected to an nbd client
 **/
void serveconnection(CLIENT *client) {
        char buf[80];
        splitexport(client);
        if (!client->server->expected_size) {
                client->exportsize = size_autodetect(client->export[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 {
                memset(buf, '\0', 80);
                snprintf(buf, 79, "%Lu", (unsigned long long)client->exportsize);
                msg3(LOG_INFO, "size of exported file/device is ", buf);
        }

        setmysockopt(client->net);

        mainloop(client);
}

/**
 * Find the name of the file we have to serve. This will use snprintf()
 * to put the IP address of the client inside a filename containing
 * "%s". That name is then written to exportname2
 *
 * @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 ;

        client->clientname=g_malloc(256);
        if (getpeername(net, (struct sockaddr *) &addrin, (socklen_t *)&addrinlen) < 0)
                err("getsockname failed: %m");
        peername = inet_ntoa(addrin.sin_addr);
        snprintf(client->exportname, 1024, client->server->exportname, peername);
        client->exportname[1023]='\0';

        msg4(LOG_INFO, "connect from %s, assigned file is %s", 
             peername, client->exportname);
        strncpy(clientname,peername,255) ;
}

/**
 * Connect the socket, and start to serve. This function will fork()
 * if a connection from an authorized client is received, and will
 * start mainloop().
 *
 * @todo modularize this giant beast. Preferably with a chainsaw. Also,
 * it has no business starting mainloop(); it should connect, and be
 * done with it.
 *
 * @param port the port where we will listen
 **/
void connectme(SERVER* serve) {
        struct sockaddr_in addrin;
        struct sigaction sa;
        int addrinlen = sizeof(addrin);
        int net, sock, newpid, i;
#ifndef sun
        int yes=1;
#else
        char yes='1';
#endif /* sun */
#ifndef NODAEMON
#ifndef NOFORK
        FILE*pidf;

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

        if ((sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
                err("socket: %m");

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

        DEBUG("Waiting for connections... bind, ");
        addrin.sin_family = AF_INET;
        addrin.sin_port = htons(serve->port);
        addrin.sin_addr.s_addr = 0;
        if (bind(sock, (struct sockaddr *) &addrin, addrinlen) < 0)
                err("bind: %m");
        DEBUG("listen, ");
        if (listen(sock, 1) < 0)
                err("listen: %m");
        DEBUG("accept, ");
        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_malloc(sizeof(pid_t)*child_arraysize);
        memset(children, 0, sizeof(pid_t)*DEFAULT_CHILD_ARRAY);
        for(;;) { /* infinite loop */
                CLIENT *client;
                if ((net = accept(sock, (struct sockaddr *) &addrin, &addrinlen)) < 0)
                        err("accept: %m");

                client = g_malloc(sizeof(CLIENT));
                client->server=serve;
                client->net=net;
                set_peername(net, client);
                if (!authorized_client(client)) {
                        msg2(LOG_INFO,"Unauthorized client") ;
                        close(net) ;
                        continue ;
                }
                msg2(LOG_INFO,"Authorized client") ;
                for(i=0;children[i]&&i<child_arraysize;i++);
                if(i>=child_arraysize) {
                        pid_t*ptr;

                        ptr=realloc(children, sizeof(pid_t)*child_arraysize);
                        if(ptr) {
                                children=ptr;
                                memset(children+child_arraysize, 0, sizeof(pid_t)*DEFAULT_CHILD_ARRAY);
                                i=child_arraysize+1;
                                child_arraysize+=DEFAULT_CHILD_ARRAY;
                        } else {
                                msg2(LOG_INFO,"Not enough memory to store child PID");
                                close(net);
                                continue;
                        }
                }
#ifndef NOFORK
                if ((children[i]=fork())<0) {
                        msg3(LOG_INFO,"Could not fork (%s)",strerror(errno)) ;
                        close(net) ;
                        continue ;
                }
                if (children[i]>0) { /* parent */
                        close(net) ; continue ; }
                /* child */
                realloc(children,0);
                child_arraysize=0;
                close(sock) ;
#endif // NOFORK
                msg2(LOG_INFO,"Starting to serve") ;
                serveconnection(client);
        }
}

/**
 * Main entry point...
 **/
int main(int argc, char *argv[]) {
        SERVER* serve;
        if (sizeof( struct nbd_request )!=28) {
                fprintf(stderr,"Bad size of structure. Alignment problems?\n");
                exit(-1) ;
        }
        logging();
        serve=cmdline(argc, argv);
        
        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;
                set_peername(0,client);
                serveconnection(0);
                return 0;
        }
        connectme(serve); /* serve infinitely */
        return 0 ;
}