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prepare-root: Switch to a tmpfs for transient root

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We're debating this over in https://github.com/CentOS/centos-bootc-dev/pull/27
and I have come to the conclusion that having changes to `/`
persist across reboot by default was a bad idea.

- It conflicts with any kind of secure boot scenario
- Having things only go away on upgrades is in some ways even *more* surprising
- The term `transient` implies this

There may be a use case in the future for having something like `root.transient = persistent`,
but this is just a better default.

Signed-off-by: Colin Walters <walters@verbum.org>
This commit is contained in:
Colin Walters 2024-02-13 15:41:35 -05:00
parent eeccac7fc9
commit 0cff65d61a
1 changed files with 18 additions and 14 deletions
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32
src/switchroot/ostree-prepare-root.c
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@ -308,17 +308,6 @@ main (int argc, char *argv[])
if (mkdirat (AT_FDCWD, OTCORE_RUN_OSTREE_PRIVATE, 0) < 0) if (mkdirat (AT_FDCWD, OTCORE_RUN_OSTREE_PRIVATE, 0) < 0)
err (EXIT_FAILURE, "Failed to create %s", OTCORE_RUN_OSTREE_PRIVATE); err (EXIT_FAILURE, "Failed to create %s", OTCORE_RUN_OSTREE_PRIVATE);
g_autofree char *transient_root_workdir = NULL;
g_autofree char *transient_root_upperdir = NULL;
if (root_transient)
{
g_autofree char *backingdir = g_strdup_printf ("../../backing/%s", deploy_directory_name);
transient_root_workdir
= g_build_filename (backingdir, OSTREE_DEPLOYMENT_ROOT_TRANSIENT_DIR, "work", NULL);
transient_root_upperdir
= g_build_filename (backingdir, OSTREE_DEPLOYMENT_ROOT_TRANSIENT_DIR, "upper", NULL);
}
/* Fall back to querying the repository configuration in the target disk. /* Fall back to querying the repository configuration in the target disk.
* This is an operating system builder choice. More info: * This is an operating system builder choice. More info:
* https://github.com/ostreedev/ostree/pull/1767 * https://github.com/ostreedev/ostree/pull/1767
@ -387,11 +376,26 @@ main (int argc, char *argv[])
g_autofree char *expected_digest = NULL; g_autofree char *expected_digest = NULL;
// For now we just stick the transient root on the default /run tmpfs;
// however, see
// https://github.com/systemd/systemd/blob/604b2001081adcbd64ee1fbe7de7a6d77c5209fe/src/basic/mountpoint-util.h#L36
// which bumps up these defaults for the rootfs a bit.
g_autofree char *root_upperdir
= root_transient ? g_build_filename (OTCORE_RUN_OSTREE_PRIVATE, "root/upper", NULL)
: NULL;
g_autofree char *root_workdir
= root_transient ? g_build_filename (OTCORE_RUN_OSTREE_PRIVATE, "root/work", NULL) : NULL;
// Propagate these options for transient root, if provided // Propagate these options for transient root, if provided
if (transient_root_upperdir) if (root_transient)
{ {
cfs_options.workdir = transient_root_workdir; if (!glnx_shutil_mkdir_p_at (AT_FDCWD, root_upperdir, 0755, NULL, &error))
cfs_options.upperdir = transient_root_upperdir; errx (EXIT_FAILURE, "Failed to create %s: %s", root_upperdir, error->message);
if (!glnx_shutil_mkdir_p_at (AT_FDCWD, root_workdir, 0700, NULL, &error))
errx (EXIT_FAILURE, "Failed to create %s: %s", root_workdir, error->message);
cfs_options.workdir = root_workdir;
cfs_options.upperdir = root_upperdir;
} }
else else
{ {