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Von: "Mickaël Salaün" mic@digikod.net hostfs creates a new inode for each opened or created file, which created useless inode allocations and forbade identifying a host file with a kernel inode.
Fix this uncommon filesystem behavior by tying kernel inodes to host file's inode and device IDs. Even if the host filesystem inodes may be recycled, this cannot happen while a file referencing it is open, which is the case with hostfs. It should be noted that hostfs inode IDs may not be unique for the same hostfs superblock because multiple host's (backed) superblocks may be used.
Delete inodes when dropping them to force backed host's file descriptors closing.
This enables to entirely remove ARCH_EPHEMERAL_INODES, and then makes Landlock fully supported by UML. This is very useful for testing (ongoing and backported) changes.
Removing ARCH_EPHEMERAL_INODES should be a patch on its own, IMHO.
These changes also factor out and simplify some helpers thanks to the new hostfs_inode_update() and the hostfs_iget() revamp: read_name(), hostfs_create(), hostfs_lookup(), hostfs_mknod(), and hostfs_fill_sb_common().
A following commit with new Landlock tests check this new hostfs inode consistency.
Cc: Anton Ivanov anton.ivanov@cambridgegreys.com Cc: Johannes Berg johannes@sipsolutions.net Cc: Richard Weinberger richard@nod.at Cc: stable@vger.kernel.org # 5.15.x: ce72750f04d6: hostfs: Fix writeback of dirty pages Cc: stable@vger.kernel.org # 5.15+
I'm not sure whether this patch qualifies as stable material. While I fully agree that the current behavoir is odd, nothing user visible is really broken so far.
Signed-off-by: Mickaël Salaün mic@digikod.net Link: https://lore.kernel.org/r/20230309165455.175131-2-mic@digikod.net
Other than that, patch looks good to me.
Thanks, //richard