Re: [PATCH v3 09/10] mm/shmem_luo: Allow retrieving tmpfs files with O_RDONLY

[Pasha Tatashin]

> Allow userspace to pass O_RDONLY in struct liveupdate_shmem_retrieve_arg
> to retrieve a tmpfs file read-only.
> 
> open() requires write access for O_TMPFILE, so create the file writable
> like before, then reopen it read-only with dentry_open() using the flags
> of the writable file, which file_open_root() normalized, and drop the
> writable file. Like open(), which grants the requested access to a new
> file regardless of its mode, don't check permission for the read-only
> open.
> 
> Retrieving a file read-only allows a restored binary to be executed
> before the session is finished. LUO keeps the retrieved file open until
> then, and executing a binary that is open for writing fails with
> -ETXTBSY. Being able to execute restored binaries right away matters
> when they are needed to finish restoring the system, e.g. to bring up
> the services that retrieve and finish the remaining sessions.
> 
> Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
> Link: https://patch.msgid.link/20261103010216.3447716-10-dmatlack@xxxxxxxxxx

Acked-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>

-- 
Pasha