ceph/src/common/compat.cc

   1 // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
   2 // vim: ts=8 sw=2 smarttab
   3
   4 #include <fcntl.h>
   5 #include <stdint.h>
   6 #include <unistd.h>
   7 #include <string.h>
   8 #include <errno.h>
   9 #include <sys/stat.h>
  10 #include <sys/param.h>
  11 #include <sys/mount.h>
  12 #if defined(__linux__)
  13 #include <sys/vfs.h>
  14 #endif
  15
  16 #include "include/compat.h"
  17 #include "common/safe_io.h"
  18
  19 // The type-value for a ZFS FS in fstatfs.
  20 #define FS_ZFS_TYPE 0xde
  21
  22 // On FreeBSD, ZFS fallocate always fails since it is considered impossible to
  23 // reserve space on a COW filesystem. posix_fallocate() returns EINVAL
  24 // Linux in this case already emulates the reservation in glibc
  25 // In which case it is allocated manually, and still that is not a real guarantee
  26 // that a full buffer is allocated on disk, since it could be compressed.
  27 // To prevent this the written buffer needs to be loaded with random data.
  28 int manual_fallocate(int fd, off_t offset, off_t len) {
  29   int r = lseek(fd, offset, SEEK_SET);
  30   if (r == -1)
  31     return errno;
  32   char data[1024*128];
  33   // TODO: compressing filesystems would require random data
  34   memset(data, 0x42, sizeof(data));
  35   for (off_t off = 0; off < len; off += sizeof(data)) {
  36     if (off + sizeof(data) > len)
  37       r = safe_write(fd, data, len - off);
  38     else
  39       r = safe_write(fd, data, sizeof(data));
  40     if (r == -1) {
  41       return errno;
  42     }
  43   }
  44   return 0;
  45 }
  46
  47 int on_zfs(int basedir_fd) {
  48   struct statfs basefs;
  49   (void)fstatfs(basedir_fd, &basefs);
  50   return (basefs.f_type == FS_ZFS_TYPE);
  51 }
  52
  53 int ceph_posix_fallocate(int fd, off_t offset, off_t len) {
  54   // Return 0 if oke, otherwise errno > 0
  55
  56 #ifdef HAVE_POSIX_FALLOCATE
  57   if (on_zfs(fd)) {
  58     return manual_fallocate(fd, offset, len);
  59   } else {
  60     return posix_fallocate(fd, offset, len);
  61   }
  62 #elif defined(__APPLE__)
  63   fstore_t store;
  64   store.fst_flags = F_ALLOCATECONTIG;
  65   store.fst_posmode = F_PEOFPOSMODE;
  66   store.fst_offset = offset;
  67   store.fst_length = len;
  68
  69   int ret = fcntl(fd, F_PREALLOCATE, &store);
  70   if (ret == -1) {
  71     ret = errno;
  72   }
  73   return ret;
  74 #else
  75   return manual_fallocate(fd, offset, len);
  76 #endif
  77 }
  78