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cp: improve hole handling on squashfs

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Better fix for problem reported by Jeremy Allison
<https://bugs.gnu.org/79267>.
* src/copy.c (struct scan_inference): New type, replacing
union scan_inference.  All uses changed.  This is so
infer_scantype can report the first hole's offset when known.
(lseek_copy): 5th arg is now struct scan_inference const *,
not just off_t.  All uses changed.
(infer_scantype): If SEEK_SET+SEEK_HOLE do not find a hole,
fall back on ZERO_SCANTYPE.
This commit is contained in:
Paul Eggert
2025-08-22 17:34:04 -07:00
parent 306de6c261
commit 39f22fe687
2 changed files with 43 additions and 21 deletions
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4
NEWS
View File

@@ -17,6 +17,10 @@ GNU coreutils NEWS -*- outline -*-
data zeros used extents rather than holes.
[This bug was present in "the beginning".]
cp missed opportunities to create holes when copying from file
systems like squashfs that support SEEK_HOLE only trivially.
[bug introduced in coreutils-9.0]
cp, install, and mv now avoid possible data corruption on
glibc 2.41 and 2.42 systems when copy_file_range is used with ranges > 2GiB,
avoiding https://sourceware.org/PR33245

60
src/copy.c
View File

@@ -106,6 +106,16 @@
# define CAN_HARDLINK_SYMLINKS 0
#endif
/* Result of infer_scantype when it returns LSEEK_SCANTYPE. */
struct scan_inference
{
/* The offset of the first data block, or -1 if the file has no data. */
off_t ext_start;
/* The offset of the first hole. */
off_t hole_start;
};
struct dir_list
{
struct dir_list *parent;
@@ -540,7 +550,7 @@ write_zeros (int fd, off_t n_bytes)
static bool
lseek_copy (int src_fd, int dest_fd, char **abuf, size_t buf_size,
off_t ext_start, off_t src_total_size,
struct scan_inference const *scan_inference, off_t src_total_size,
enum Sparse_type sparse_mode,
bool allow_reflink,
char const *src_name, char const *dst_name,
@@ -552,9 +562,11 @@ lseek_copy (int src_fd, int dest_fd, char **abuf, size_t buf_size,
copy_debug.sparse_detection = COPY_DEBUG_EXTERNAL;
while (0 <= ext_start)
for (off_t ext_start = scan_inference->ext_start; 0 <= ext_start; )
{
off_t ext_end = lseek (src_fd, ext_start, SEEK_HOLE);
off_t ext_end = (ext_start == 0
? scan_inference->hole_start
: lseek (src_fd, ext_start, SEEK_HOLE));
if (ext_end < 0)
{
if (errno != ENXIO)
@@ -1085,23 +1097,13 @@ enum scantype
LSEEK_SCANTYPE,
};
/* Result of infer_scantype. */
union scan_inference
{
/* Used if infer_scantype returns LSEEK_SCANTYPE. This is the
offset of the first data block, or -1 if the file has no data. */
off_t ext_start;
};
/* Return how to scan a file with descriptor FD and stat buffer SB.
*SCAN_INFERENCE is set to a valid value if returning LSEEK_SCANTYPE. */
Set *SCAN_INFERENCE if returning LSEEK_SCANTYPE. */
static enum scantype
infer_scantype (int fd, struct stat const *sb,
union scan_inference *scan_inference)
struct scan_inference *scan_inference)
{
scan_inference->ext_start = -1; /* avoid -Wmaybe-uninitialized */
/* Only attempt SEEK_HOLE if this heuristic
/* Try SEEK_HOLE only if this heuristic
suggests the file is sparse. */
if (! (HAVE_STRUCT_STAT_ST_BLOCKS
&& S_ISREG (sb->st_mode)
@@ -1109,10 +1111,26 @@ infer_scantype (int fd, struct stat const *sb,
return PLAIN_SCANTYPE;
#ifdef SEEK_HOLE
off_t ext_start = lseek (fd, 0, SEEK_DATA);
if (0 <= ext_start || errno == ENXIO)
scan_inference->ext_start = lseek (fd, 0, SEEK_DATA);
if (scan_inference->ext_start == 0)
{
scan_inference->ext_start = ext_start;
scan_inference->hole_start = lseek (fd, 0, SEEK_HOLE);
if (0 <= scan_inference->hole_start)
{
if (scan_inference->hole_start < sb->st_size)
return LSEEK_SCANTYPE;
/* Though the file likely has holes, SEEK_DATA and SEEK_HOLE
didn't find any. This can happen with file systems like
circa-2025 squashfs that support SEEK_HOLE only trivially.
Fall back on ZERO_SCANTYPE. */
if (lseek (fd, 0, SEEK_SET) < 0)
return ERROR_SCANTYPE;
}
}
else if (0 < scan_inference->ext_start || errno == ENXIO)
{
scan_inference->hole_start = 0; /* Pacify -Wmaybe-uninitialized. */
return LSEEK_SCANTYPE;
}
else if (errno != EINVAL && !is_ENOTSUP (errno))
@@ -1209,7 +1227,6 @@ copy_reg (char const *src_name, char const *dst_name,
mode_t extra_permissions;
struct stat sb;
struct stat src_open_sb;
union scan_inference scan_inference;
bool return_val = true;
bool data_copy_required = x->data_copy_required;
bool preserve_xattr = USE_XATTR & x->preserve_xattr;
@@ -1518,6 +1535,7 @@ copy_reg (char const *src_name, char const *dst_name,
size_t buf_size = io_blksize (&sb);
/* Deal with sparse files. */
struct scan_inference scan_inference;
enum scantype scantype = infer_scantype (source_desc, &src_open_sb,
&scan_inference);
if (scantype == ERROR_SCANTYPE)
@@ -1565,7 +1583,7 @@ copy_reg (char const *src_name, char const *dst_name,
#ifdef SEEK_HOLE
scantype == LSEEK_SCANTYPE
? lseek_copy (source_desc, dest_desc, &buf, buf_size,
scan_inference.ext_start, src_open_sb.st_size,
&scan_inference, src_open_sb.st_size,
make_holes ? x->sparse_mode : SPARSE_NEVER,
x->reflink_mode != REFLINK_NEVER,
src_name, dst_name, &hole_size, &n_read)