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/* extent-scan.c -- core functions for scanning extents
Copyright (C) 2010-2011 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
Written by Jie Liu (jeff.liu@oracle.com). */
#include <config.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/utsname.h>
#include <assert.h>
#include "system.h"
#include "extent-scan.h"
#include "xstrtol.h"
#ifndef HAVE_FIEMAP
# include "fiemap.h"
#endif
/* Work around Linux kernel issues on BTRFS and EXT4 before 2.6.39.
FIXME: remove in 2013, or whenever we're pretty confident
that the offending, unpatched kernels are no longer in use. */
static bool
extent_need_sync (void)
{
static int need_sync = -1;
if (need_sync == -1)
{
struct utsname name;
need_sync = 0; /* No workaround by default. */
#ifdef __linux__
if (uname (&name) != -1 && STRNCMP_LIT (name.release, "2.6.") == 0)
{
unsigned long val;
if (xstrtoul (name.release + 4, NULL, 10, &val, NULL) == LONGINT_OK)
{
if (val < 39)
need_sync = 1;
}
}
#endif
}
return need_sync;
}
/* Allocate space for struct extent_scan, initialize the entries if
necessary and return it as the input argument of extent_scan_read(). */
extern void
extent_scan_init (int src_fd, struct extent_scan *scan)
{
scan->fd = src_fd;
scan->ei_count = 0;
scan->scan_start = 0;
scan->initial_scan_failed = false;
scan->hit_final_extent = false;
scan->fm_flags = extent_need_sync () ? FIEMAP_FLAG_SYNC : 0;
}
#ifdef __linux__
# ifndef FS_IOC_FIEMAP
# define FS_IOC_FIEMAP _IOWR ('f', 11, struct fiemap)
# endif
/* Call ioctl(2) with FS_IOC_FIEMAP (available in linux 2.6.27) to
obtain a map of file extents excluding holes. */
extern bool
extent_scan_read (struct extent_scan *scan)
{
union { struct fiemap f; char c[4096]; } fiemap_buf;
struct fiemap *fiemap = &fiemap_buf.f;
struct fiemap_extent *fm_extents = &fiemap->fm_extents[0];
enum { count = (sizeof fiemap_buf - sizeof *fiemap) / sizeof *fm_extents };
verify (count != 0);
/* This is required at least to initialize fiemap->fm_start,
but also serves (in mid 2010) to appease valgrind, which
appears not to know the semantics of the FIEMAP ioctl. */
memset (&fiemap_buf, 0, sizeof fiemap_buf);
fiemap->fm_start = scan->scan_start;
fiemap->fm_flags = scan->fm_flags;
fiemap->fm_extent_count = count;
fiemap->fm_length = FIEMAP_MAX_OFFSET - scan->scan_start;
/* Fall back to the standard copy if call ioctl(2) failed for the
the first time. */
if (ioctl (scan->fd, FS_IOC_FIEMAP, fiemap) < 0)
{
if (scan->scan_start == 0)
scan->initial_scan_failed = true;
return false;
}
/* If 0 extents are returned, then more get_extent_table() are not needed. */
if (fiemap->fm_mapped_extents == 0)
{
scan->hit_final_extent = true;
return false;
}
scan->ei_count = fiemap->fm_mapped_extents;
scan->ext_info = xnmalloc (scan->ei_count, sizeof (struct extent_info));
unsigned int i, si = 0;
struct extent_info *last_ei IF_LINT ( = scan->ext_info);
for (i = 0; i < scan->ei_count; i++)
{
assert (fm_extents[i].fe_logical <= OFF_T_MAX - fm_extents[i].fe_length);
if (si && last_ei->ext_flags ==
(fm_extents[i].fe_flags & ~FIEMAP_EXTENT_LAST)
&& (last_ei->ext_logical + last_ei->ext_length
== fm_extents[i].fe_logical))
{
/* Merge previous with last. */
last_ei->ext_length += fm_extents[i].fe_length;
/* Copy flags in case different. */
last_ei->ext_flags = fm_extents[i].fe_flags;
}
else if ((si == 0 && scan->scan_start > fm_extents[i].fe_logical)
|| (si && last_ei->ext_logical + last_ei->ext_length >
fm_extents[i].fe_logical))
{
/* BTRFS before 2.6.38 could return overlapping extents
for sparse files. We adjust the returned extents
rather than failing, as otherwise it would be inefficient
to detect this on the initial scan. */
uint64_t new_logical;
uint64_t length_adjust;
if (si == 0)
new_logical = scan->scan_start;
else
{
/* We could return here if scan->scan_start == 0
but don't so as to minimize special cases. */
new_logical = last_ei->ext_logical + last_ei->ext_length;
}
length_adjust = new_logical - fm_extents[i].fe_logical;
/* If an extent is contained within the previous one, just fail. */
if (length_adjust < fm_extents[i].fe_length)
{
if (scan->scan_start == 0)
scan->initial_scan_failed = true;
return false;
}
fm_extents[i].fe_logical = new_logical;
fm_extents[i].fe_length -= length_adjust;
/* Process the adjusted extent again. */
i--;
continue;
}
else
{
last_ei = scan->ext_info + si;
last_ei->ext_logical = fm_extents[i].fe_logical;
last_ei->ext_length = fm_extents[i].fe_length;
last_ei->ext_flags = fm_extents[i].fe_flags;
si++;
}
}
/* We don't bother reallocating. We should though if we change
to looping through all extents, within this function. */
scan->ei_count = si;
if (last_ei->ext_flags & FIEMAP_EXTENT_LAST)
scan->hit_final_extent = true;
else
scan->scan_start = last_ei->ext_logical + last_ei->ext_length;
return true;
}
#else
extern bool
extent_scan_read (struct extent_scan *scan ATTRIBUTE_UNUSED)
{
scan->initial_scan_failed = true;
errno = ENOTSUP;
return false;
}
#endif
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