[PATCH v3] rootfs: Fix support for rootfstype= when root= is given

Stefan Berger
2023-11-20T01:13:07Z

Documentation/filesystems/ramfs-rootfs-initramfs.rst states:

If CONFIG_TMPFS is enabled, rootfs will use tmpfs instead of ramfs by
default. To force ramfs, add "rootfstype=ramfs" to the kernel command
line.

This currently does not work when root= is provided since then
saved_root_name contains a string and rootfstype= is ignored. Therefore,
ramfs is currently always chosen when root= is provided.

The current behavior for rootfs's filesystem is:

root= | rootfstype= | chosen rootfs filesystem
------------+-------------+--------------------------
unspecified | unspecified | tmpfs
unspecified | tmpfs | tmpfs
unspecified | ramfs | ramfs
provided | ignored | ramfs

rootfstype= should be respected regardless whether root= is given,
as shown below:

root= | rootfstype= | chosen rootfs filesystem
------------+-------------+--------------------------
unspecified | unspecified | tmpfs (as before)
unspecified | tmpfs | tmpfs (as before)
unspecified | ramfs | ramfs (as before)
provided | unspecified | ramfs (compatibility with before)
provided | tmpfs | tmpfs (new)
provided | ramfs | ramfs (new)

This table represents the new behavior.

Fixes: 6e19eded3684 ("initmpfs: use initramfs if rootfstype= or root= specified")
Cc: <stable@vger.kernel.org>
Signed-off-by: Rob Landley <rob@landley.net>
Link: https://lore.kernel.org/lkml/8244c75f-445e-b15b-9dbf-266e7ca666e2@landley.net/
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>

---

v3:
- Changed initfstype= to rootfstype=
- Remove my R-b

v2:
- Cc'ing stable mailing list now
---
init/do_mounts.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 5fdef94f0864..279ad28bf4fb 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -510,7 +510,10 @@ struct file_system_type rootfs_fs_type = {

void __init init_rootfs(void)
{
- if (IS_ENABLED(CONFIG_TMPFS) && !saved_root_name[0] &&
- (!root_fs_names || strstr(root_fs_names, "tmpfs")))
- is_tmpfs = true;
+ if (IS_ENABLED(CONFIG_TMPFS)) {
+ if (!saved_root_name[0] && !root_fs_names)
+ is_tmpfs = true;
+ else if (root_fs_names && !!strstr(root_fs_names, "tmpfs"))
+ is_tmpfs = true;
+ }
}
--
2.41.0