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sysupdate: Support volatile-root for finding the root partition

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The existing logic can't find the root device in scenarios where
the root has been replaced with an overlay. We support looking
at "/run/systemd/volatile-root" to find the original root, similar
to what systemd-repart and gpt-auto-generator do.
This commit is contained in:
reuben olinsky
2022-10-31 22:58:52 -07:00
committed by Lennart Poettering
parent d995ccd7b5
commit f8a7112c47
1 changed files with 18 additions and 4 deletions
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22
src/sysupdate/sysupdate-resource.c
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@@ -8,6 +8,7 @@
#include "blockdev-util.h"
#include "chase-symlinks.h"
#include "device-util.h"
#include "devnum-util.h"
#include "dirent-util.h"
#include "env-util.h"
#include "fd-util.h"
@@ -525,10 +526,14 @@ int resource_resolve_path(
assert(rr);
if (rr->path_auto) {
struct stat orig_root_stats;
/* NB: we don't actually check the backing device of the root fs "/", but of "/usr", in order
* to support environments where the root fs is a tmpfs, and the OS itself placed exclusively
* in /usr/. */
/* NB: If the root mount has been replaced by some form of volatile file system (overlayfs),
* the original root block device node is symlinked in /run/systemd/volatile-root. Let's
* follow that link here. If that doesn't exist, we check the backing device of "/usr". We
* don't actually check the backing device of the root fs "/", in order to support
* environments where the root fs is a tmpfs, and the OS itself placed exclusively in
* /usr/. */
if (rr->type != RESOURCE_PARTITION)
return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
@@ -546,7 +551,16 @@ int resource_resolve_path(
return log_error_errno(SYNTHETIC_ERRNO(EPERM),
"Block device is not allowed when using --root= mode.");
r = get_block_device_harder("/usr/", &d);
r = stat("/run/systemd/volatile-root", &orig_root_stats);
if (r < 0) {
if (errno == -ENOENT) /* volatile-root not found */
r = get_block_device_harder("/usr/", &d);
else
return log_error_errno(r, "Failed to stat /run/systemd/volatile-root: %m");
} else if (!S_ISBLK(orig_root_stats.st_mode)) /* symlink was present but not block device */
return log_error_errno(SYNTHETIC_ERRNO(ENOTBLK), "/run/systemd/volatile-root is not linked to a block device.");
else /* symlink was present and a block device */
d = orig_root_stats.st_rdev;
} else if (rr->type == RESOURCE_PARTITION) {
_cleanup_close_ int fd = -1, real_fd = -1;