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gpt-auto-generator: Use volatile-root by default and automatic logic as fallback #20578

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merged 1 commit into from Aug 31, 2021
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gpt-auto-generator: Use volatile-root by default and automatic logic as fallback #20578

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5 changes: 5 additions & 0 deletions man/systemd-gpt-auto-generator.xml
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Expand Up @@ -228,6 +228,11 @@
For more information, see <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>

<para>The root partition can be specified by symlinking <filename>/run/systemd/volatile-root</filename>
to <filename>/dev/block/$major:$minor</filename>. This is especially useful if the root mount has been
replaced by some form of volatile file system (overlayfs).
</para>

<para>Mount and automount units for the EFI System Partition (ESP) are generated on EFI systems. The ESP
is mounted to <filename>/boot/</filename> (except if an Extended Boot Loader partition exists, see
below), unless a mount point directory <filename>/efi/</filename> exists, in which case it is mounted
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53 changes: 24 additions & 29 deletions src/gpt-auto-generator/gpt-auto-generator.c
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Expand Up @@ -764,41 +764,36 @@ static int enumerate_partitions(dev_t devnum) {
}

static int add_mounts(void) {
dev_t devno;
_cleanup_free_ char *p = NULL;
int r;
dev_t devno;

r = get_block_device_harder("/", &devno);
if (r == -EUCLEAN)
return btrfs_log_dev_root(LOG_ERR, r, "root file system");
if (r < 0)
return log_error_errno(r, "Failed to determine block device of root file system: %m");
if (r == 0) { /* Not backed by block device */
r = get_block_device_harder("/usr", &devno);
/* If the root mount has been replaced by some form of volatile file system (overlayfs), the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 read that
* here. */
r = readlink_malloc("/run/systemd/volatile-root", &p);
if (r == -ENOENT) { /* volatile-root not found */
r = get_block_device_harder("/", &devno);
if (r == -EUCLEAN)
return btrfs_log_dev_root(LOG_ERR, r, "/usr");
return btrfs_log_dev_root(LOG_ERR, r, "root file system");
if (r < 0)
return log_error_errno(r, "Failed to determine block device of /usr file system: %m");
if (r == 0) {
_cleanup_free_ char *p = NULL;
mode_t m;

/* 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 read that
* here. */
r = readlink_malloc("/run/systemd/volatile-root", &p);
if (r == -ENOENT) {
log_debug("Neither root nor /usr file system are on a (single) block device.");
return 0;
}
return log_error_errno(r, "Failed to determine block device of root file system: %m");
if (r == 0) { /* Not backed by block device */
r = get_block_device_harder("/usr", &devno);
if (r == -EUCLEAN)
return btrfs_log_dev_root(LOG_ERR, r, "/usr");
if (r < 0)
return log_error_errno(r, "Failed to read symlink /run/systemd/volatile-root: %m");

r = device_path_parse_major_minor(p, &m, &devno);
if (r < 0)
return log_error_errno(r, "Failed to parse major/minor device node: %m");
if (!S_ISBLK(m))
return log_error_errno(SYNTHETIC_ERRNO(ENOTBLK), "Volatile root device is of wrong type.");
return log_error_errno(r, "Failed to determine block device of /usr file system: %m");
}
} else if (r < 0)
return log_error_errno(r, "Failed to read symlink /run/systemd/volatile-root: %m");
else {
mode_t m;
r = device_path_parse_major_minor(p, &m, &devno);
if (r < 0)
return log_error_errno(r, "Failed to parse major/minor device node: %m");
if (!S_ISBLK(m))
return log_error_errno(SYNTHETIC_ERRNO(ENOTBLK), "Volatile root device is of wrong type.");
}

return enumerate_partitions(devno);
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