From bab8c851daaa2a4ed9febb7cc958f701ee024151 Mon Sep 17 00:00:00 2001 From: Yu Watanabe Date: Mon, 27 May 2024 06:01:05 +0900 Subject: [PATCH] blockdev-util: also check loop/partscan sysattr With https://github.com/torvalds/linux/commit/b9684a71fca793213378dd410cd11675d973eaa1 (v5.19), we cannot check partition scanning is enabled for a loopback block device without checking the attribute. --- src/shared/blockdev-util.c | 33 ++++++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-) diff --git a/src/shared/blockdev-util.c b/src/shared/blockdev-util.c index caab14ab38b..322e5280cdf 100644 --- a/src/shared/blockdev-util.c +++ b/src/shared/blockdev-util.c @@ -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 -- 2.47.3