src/extent-scan.c

   1 /* extent-scan.c -- core functions for scanning extents
   2    Copyright (C) 2010 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16
  17    Written by Jie Liu (jeff.liu@oracle.com).  */
  18
  19 #include <config.h>
  20 #include <stdio.h>
  21 #include <sys/types.h>
  22 #include <sys/ioctl.h>
  23 #include <assert.h>
  24
  25 #include "system.h"
  26 #include "extent-scan.h"
  27
  28 #ifndef HAVE_FIEMAP
  29 # include "fiemap.h"
  30 #endif
  31
  32 /* Allocate space for struct extent_scan, initialize the entries if
  33    necessary and return it as the input argument of extent_scan_read().  */
  34 extern void
  35 extent_scan_init (int src_fd, struct extent_scan *scan)
  36 {
  37   scan->fd = src_fd;
  38   scan->ei_count = 0;
  39   scan->scan_start = 0;
  40   scan->initial_scan_failed = false;
  41   scan->hit_final_extent = false;
  42 }
  43
  44 #ifdef __linux__
  45 # ifndef FS_IOC_FIEMAP
  46 #  define FS_IOC_FIEMAP _IOWR ('f', 11, struct fiemap)
  47 # endif
  48 /* Call ioctl(2) with FS_IOC_FIEMAP (available in linux 2.6.27) to
  49    obtain a map of file extents excluding holes.  */
  50 extern bool
  51 extent_scan_read (struct extent_scan *scan)
  52 {
  53   union { struct fiemap f; char c[4096]; } fiemap_buf;
  54   struct fiemap *fiemap = &fiemap_buf.f;
  55   struct fiemap_extent *fm_extents = &fiemap->fm_extents[0];
  56   enum { count = (sizeof fiemap_buf - sizeof *fiemap) / sizeof *fm_extents };
  57   verify (count != 0);
  58
  59   /* This is required at least to initialize fiemap->fm_start,
  60      but also serves (in mid 2010) to appease valgrind, which
  61      appears not to know the semantics of the FIEMAP ioctl. */
  62   memset (&fiemap_buf, 0, sizeof fiemap_buf);
  63
  64   fiemap->fm_start = scan->scan_start;
  65   fiemap->fm_flags = FIEMAP_FLAG_SYNC;
  66   fiemap->fm_extent_count = count;
  67   fiemap->fm_length = FIEMAP_MAX_OFFSET - scan->scan_start;
  68
  69   /* Fall back to the standard copy if call ioctl(2) failed for the
  70      the first time.  */
  71   if (ioctl (scan->fd, FS_IOC_FIEMAP, fiemap) < 0)
  72     {
  73       if (scan->scan_start == 0)
  74         scan->initial_scan_failed = true;
  75       return false;
  76     }
  77
  78   /* If 0 extents are returned, then more get_extent_table() are not needed.  */
  79   if (fiemap->fm_mapped_extents == 0)
  80     {
  81       scan->hit_final_extent = true;
  82       return false;
  83     }
  84
  85   scan->ei_count = fiemap->fm_mapped_extents;
  86   scan->ext_info = xnmalloc (scan->ei_count, sizeof (struct extent_info));
  87
  88   unsigned int i;
  89   for (i = 0; i < scan->ei_count; i++)
  90     {
  91       assert (fm_extents[i].fe_logical <= OFF_T_MAX);
  92
  93       scan->ext_info[i].ext_logical = fm_extents[i].fe_logical;
  94       scan->ext_info[i].ext_length = fm_extents[i].fe_length;
  95       scan->ext_info[i].ext_flags = fm_extents[i].fe_flags;
  96     }
  97
  98   i--;
  99   if (scan->ext_info[i].ext_flags & FIEMAP_EXTENT_LAST)
 100     {
 101       scan->hit_final_extent = true;
 102       return true;
 103     }
 104
 105   scan->scan_start = fm_extents[i].fe_logical + fm_extents[i].fe_length;
 106
 107   return true;
 108 }
 109 #else
 110 extern bool
 111 extent_scan_read (struct extent_scan *scan ATTRIBUTE_UNUSED)
 112 {
 113   errno = ENOTSUP;
 114   return false;
 115 }
 116 #endif