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blockdev-util: also check loop/partscan sysattr

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With b9684a71fc (v5.19),
we cannot check partition scanning is enabled for a loopback block device
without checking the attribute.
This commit is contained in:
Yu Watanabe
2024-05-27 06:01:05 +09:00
parent f0c2668c99
commit bab8c851da
1 changed files with 26 additions and 7 deletions
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33
src/shared/blockdev-util.c
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@@ -383,16 +383,29 @@ int blockdev_partscan_enabled(int fd) {
* e81cd5a983bb35dabd38ee472cf3fea1c63e0f23, the flag was never used. So, fortunately, we can use
* both the new and old values safely.
*
* With https://github.com/torvalds/linux/commit/b9684a71fca793213378dd410cd11675d973eaa1 (v5.19),
* another flag GD_SUPPRESS_PART_SCAN is introduced for loopback block device, and partition scanning
* is done only when both GENHD_FL_NO_PART and GD_SUPPRESS_PART_SCAN are not set. Before the commit,
* LO_FLAGS_PARTSCAN flag was directly tied with GENHD_FL_NO_PART. But with this change now it is
* tied with GD_SUPPRESS_PART_SCAN. So, LO_FLAGS_PARTSCAN cannot be obtained from 'ext_range'
* sysattr, which corresponds to GENHD_FL_NO_PART, and we need to read 'loop/partscan'. 💣💣💣
*
* With https://github.com/torvalds/linux/commit/73a166d9749230d598320fdae3b687cdc0e2e205 (v6.3),
* the GD_SUPPRESS_PART_SCAN flag is also introduced for userspace block device (ublk). Though, not
* sure if we should support the device...
*
* With https://github.com/torvalds/linux/commit/e81cd5a983bb35dabd38ee472cf3fea1c63e0f23 (v6.3),
* the 'capability' sysfs attribute is deprecated, hence we cannot check the flag from it.
* the 'capability' sysfs attribute is deprecated, hence we cannot check flags from it. 💣💣💣
*
* With https://github.com/torvalds/linux/commit/a4217c6740dc64a3eb6815868a9260825e8c68c6
* (backported to v6.9), the partscan status is directly exposed as 'partscan' sysattr.
* With https://github.com/torvalds/linux/commit/a4217c6740dc64a3eb6815868a9260825e8c68c6 (v6.10,
* backported to v6.9), the partscan status is directly exposed as 'partscan' sysattr.
*
* To support both old and new kernels, we need to do the following: first check 'partscan' attr
* where the information is made directly available; then, fall back to 'ext_range' sysfs attribute,
* and if '1' we can conclude partition scanning is disabled; otherwise check 'capability' sysattr
* for ancient version. */
* To support both old and new kernels, we need to do the following:
* 1) check 'partscan' sysfs attribute where the information is made directly available,
* 2) check 'loop/partscan' sysfs attribute for loopback block devices, and if '0' we can conclude
* partition scanning is disabled,
* 3) check 'ext_range' sysfs attribute, and if '1' we can conclude partition scanning is disabled,
* 4) otherwise check 'capability' sysfs attribute for ancient version. */
assert(fd >= 0);
@@ -400,10 +413,16 @@ int blockdev_partscan_enabled(int fd) {
if (r < 0)
return r;
/* For v6.10 or newer. */
r = device_get_sysattr_bool(dev, "partscan");
if (r != -ENOENT)
return r;
/* For loopback block device, especially for v5.19 or newer. Even if this is enabled, we also need to
* check GENHD_FL_NO_PART flag through 'ext_range' and 'capability' sysfs attributes below. */
if (device_get_sysattr_bool(dev, "loop/partscan") == 0)
return false;
r = device_get_sysattr_int(dev, "ext_range", &ext_range);
if (r == -ENOENT) /* If the ext_range file doesn't exist then we are most likely looking at a
* partition block device, not the whole block device. And that means we have no