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virtiofsd: Store every lo_inode's parent_dev 

We want to detect mount points in the shared tree.  We report them to
the guest by setting the FUSE_ATTR_SUBMOUNT flag in fuse_attr.flags, but
because the FUSE client will create a submount for every directory that
has this flag set, we must do this only for the actual mount points.

We can detect mount points by comparing a directory's st_dev with its
parent's st_dev.  To be able to do so, we need to store the parent's
st_dev in the lo_inode object.

Note that mount points need not necessarily be directories; a single
file can be a mount point as well.  However, for the sake of simplicity
let us ignore any non-directory mount points for now.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200909184028.262297-6-mreitz@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Max Reitz 2020-09-09 20:40:25 +02:00 committed by Dr. David Alan Gilbert
parent ede24b6be7
commit eba8b096c1
1 changed files with 17 additions and 0 deletions
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17
tools/virtiofsd/passthrough_ll.c
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@ -125,6 +125,14 @@ struct lo_inode {
GHashTable *posix_locks; /* protected by lo_inode->plock_mutex */
mode_t filetype;
/*
* So we can detect crossmount roots
* (As such, this only needs to be valid for directories. Note
* that files can have multiple parents due to hard links, and so
* their parent_dev may fluctuate.)
*/
dev_t parent_dev;
};
struct lo_cred {
@ -847,6 +855,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
g_hash_table_insert(lo->inodes, &inode->key, inode);
pthread_mutex_unlock(&lo->mutex);
}
inode->parent_dev = dir->key.dev;
e->ino = inode->fuse_ino;
lo_inode_put(lo, &inode);
lo_inode_put(lo, &dir);
@ -1073,6 +1082,14 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent,
fuse_log(FUSE_LOG_DEBUG, " %lli/%s -> %lli\n", (unsigned long long)parent,
name, (unsigned long long)e.ino);
/*
* No need to update inode->parent_dev, because
* (1) We cannot, the inode now has more than one parent,
* (2) Directories cannot have more than one parent, so link()
* does not work for them; but parent_dev only needs to be
* valid for directories.
*/
fuse_reply_entry(req, &e);
lo_inode_put(lo, &parent_inode);
lo_inode_put(lo, &inode);