lib/dpkg/fdio.c

   1 /*
   2  * libdpkg - Debian packaging suite library routines
   3  * fdio.c - safe file descriptor based input/output
   4  *
   5  * Copyright © 2009-2010 Guillem Jover <guillem@debian.org>
   6  *
   7  * This is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  19  */
  20
  21 #include <config.h>
  22 #include <compat.h>
  23
  24 #include <errno.h>
  25 #include <fcntl.h>
  26 #include <unistd.h>
  27
  28 #include <dpkg/fdio.h>
  29
  30 ssize_t
  31 fd_read(int fd, void *buf, size_t len)
  32 {
  33         ssize_t total = 0;
  34         char *ptr = buf;
  35
  36         while (len > 0) {
  37                 ssize_t n;
  38
  39                 n = read(fd, ptr + total, len);
  40                 if (n == -1) {
  41                         if (errno == EINTR || errno == EAGAIN)
  42                                 continue;
  43                         return total ? -total : n;
  44                 }
  45                 if (n == 0)
  46                         break;
  47
  48                 total += n;
  49                 len -= n;
  50         }
  51
  52         return total;
  53 }
  54
  55 ssize_t
  56 fd_write(int fd, const void *buf, size_t len)
  57 {
  58         ssize_t total = 0;
  59         const char *ptr = buf;
  60
  61         while (len > 0) {
  62                 ssize_t n;
  63
  64                 n = write(fd, ptr + total, len);
  65                 if (n == -1) {
  66                         if (errno == EINTR || errno == EAGAIN)
  67                                 continue;
  68                         return total ? -total : n;
  69                 }
  70                 if (n == 0)
  71                         break;
  72
  73                 total += n;
  74                 len -= n;
  75         }
  76
  77         return total;
  78 }
  79
  80 #ifdef USE_DISK_PREALLOCATE
  81 #ifdef HAVE_F_PREALLOCATE
  82 static void
  83 fd_preallocate_setup(fstore_t *fs, int flags, off_t offset, off_t len)
  84 {
  85         fs->fst_flags = flags;
  86         fs->fst_posmode = F_PEOFPOSMODE;
  87         fs->fst_offset = offset;
  88         fs->fst_length = len;
  89         fs->fst_bytesalloc = 0;
  90 }
  91 #endif
  92
  93 /**
  94  * Request the kernel to allocate the specified size for a file descriptor.
  95  *
  96  * We only want to send a hint that we will be using the requested size. But
  97  * we do not want to unnecessarily write the file contents. That is why we
  98  * are not using posix_fallocate(3) directly if possible, and not at all
  99  * on glibc based systems (except on GNU/kFreeBSD).
 100  */
 101 int
 102 fd_allocate_size(int fd, off_t offset, off_t len)
 103 {
 104         int rc;
 105
 106         /* Do not preallocate on very small files as that degrades performance
 107          * on some filesystems. */
 108         if (len < (4 * 4096) - 1)
 109                 return 0;
 110
 111 #if defined(HAVE_F_PREALLOCATE)
 112         /* On Mac OS X. */
 113         fstore_t fs;
 114
 115         fd_preallocate_setup(&fs, F_ALLOCATECONTIG, offset, len);
 116         rc = fcntl(fd, F_PREALLOCATE, &fs);
 117         if (rc < 0 && errno == ENOSPC) {
 118                 /* If we cannot get a contiguous allocation, then try
 119                  * non-contiguous. */
 120                 fd_preallocate_setup(&fs, F_ALLOCATEALL, offset, len);
 121                 rc = fcntl(fd, F_PREALLOCATE, &fs);
 122         }
 123 #elif defined(HAVE_F_ALLOCSP64)
 124         /* On Solaris. */
 125         struct flock64 fl;
 126
 127         fl.l_whence = SEEK_SET;
 128         fl.l_start = offset;
 129         fl.l_len = len;
 130
 131         rc = fcntl(fd, F_ALLOCSP64, &fl);
 132 #elif defined(HAVE_FALLOCATE)
 133         /* On Linux. */
 134         do {
 135                 rc = fallocate(fd, 0, offset, len);
 136         } while (rc < 0 && errno == EINTR);
 137 #elif defined(HAVE_POSIX_FALLOCATE) && \
 138       ((defined(__GLIBC__) && defined(__FreeBSD_kernel__)) || \
 139        !defined(__GLIBC__))
 140         /*
 141          * On BSDs, newer GNU/kFreeBSD and other non-glibc based systems
 142          * we can use posix_fallocate(2) which should be a simple syscall
 143          * wrapper. But not on other glibc systems, as there the function
 144          * will try to allocate the size by writing a '\0' to each block
 145          * if the syscall is not implemented or not supported by the
 146          * kernel or the filesystem, which we do not want.
 147          */
 148         rc = posix_fallocate(fd, offset, len);
 149 #else
 150         errno = ENOSYS;
 151         rc = -1;
 152 #endif
 153
 154         return rc;
 155 }
 156 #else
 157 int
 158 fd_allocate_size(int fd, off_t offset, off_t len)
 159 {
 160         errno = ENOSYS;
 161         return -1;
 162 }
 163 #endif