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loop-util: mirror discard limits from backing device

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This commit is contained in:
nkraetzschmar
2025-10-16 00:12:50 +02:00
committed by Lennart Poettering
parent d19294e92a
commit 29ee9c6fb7
1 changed files with 51 additions and 0 deletions
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51
src/shared/loop-util.c
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@@ -375,6 +375,44 @@ static int loop_configure(
return 0;
}
static int fd_get_max_discard(int fd, uint64_t *ret) {
struct stat st;
char sysfs_path[STRLEN("/sys/dev/block/" ":" "/queue/discard_max_bytes") + DECIMAL_STR_MAX(dev_t) * 2 + 1];
_cleanup_free_ char *buffer = NULL;
int r;
assert(ret);
if (fstat(ASSERT_FD(fd), &st) < 0)
return -errno;
if (!S_ISBLK(st.st_mode))
return -ENOTBLK;
xsprintf(sysfs_path, "/sys/dev/block/" DEVNUM_FORMAT_STR "/queue/discard_max_bytes", DEVNUM_FORMAT_VAL(st.st_rdev));
r = read_one_line_file(sysfs_path, &buffer);
if (r < 0)
return r;
return safe_atou64(buffer, ret);
}
static int fd_set_max_discard(int fd, uint64_t max_discard) {
struct stat st;
char sysfs_path[STRLEN("/sys/dev/block/" ":" "/queue/discard_max_bytes") + DECIMAL_STR_MAX(dev_t) * 2 + 1];
if (fstat(ASSERT_FD(fd), &st) < 0)
return -errno;
if (!S_ISBLK(st.st_mode))
return -ENOTBLK;
xsprintf(sysfs_path, "/sys/dev/block/" DEVNUM_FORMAT_STR "/queue/discard_max_bytes", DEVNUM_FORMAT_VAL(st.st_rdev));
return write_string_filef(sysfs_path, WRITE_STRING_FILE_DISABLE_BUFFER, "%" PRIu64, max_discard);
}
static int loop_device_make_internal(
const char *path,
int fd,
@@ -572,6 +610,19 @@ static int loop_device_make_internal(
(void) usleep_safe(usec);
}
if (S_ISBLK(st.st_mode)) {
uint64_t discard_max_bytes;
r = fd_get_max_discard(fd, &discard_max_bytes);
if (r < 0)
log_debug_errno(r, "Failed to read 'discard_max_bytes' of backing device, ignoring: %m");
else {
r = fd_set_max_discard(d->fd, discard_max_bytes);
if (r < 0)
log_debug_errno(r, "Failed to write 'discard_max_bytes' of loop device, ignoring: %m");
}
}
d->backing_file = TAKE_PTR(backing_file);
d->backing_inode = st.st_ino;
d->backing_devno = st.st_dev;