fs: change d_compare for rcu-walk

Change d_compare so it may be called from lock-free RCU lookups. This
does put significant restrictions on what may be done from the callback,
however there don't seem to have been any problems with in-tree fses.
If some strange use case pops up that _really_ cannot cope with the
rcu-walk rules, we can just add new rcu-unaware callbacks, which would
cause name lookup to drop out of rcu-walk mode.

For in-tree filesystems, this is just a mechanical change.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

1 files changed, 8 insertions, 6 deletions

diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index 3345aabd1dd7..99d3c7ac973c 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -164,16 +164,18 @@ static int msdos_hash(struct dentry *dentry, struct qstr *qstr)
  * Compare two msdos names. If either of the names are invalid,
  * we fall back to doing the standard name comparison.
  */
-static int msdos_cmp(struct dentry *dentry, struct qstr *a, struct qstr *b)
+static int msdos_cmp(const struct dentry *parent, const struct inode *pinode,
+                const struct dentry *dentry, const struct inode *inode,
+                unsigned int len, const char *str, const struct qstr *name)
 {
-        struct fat_mount_options *options = &MSDOS_SB(dentry->d_sb)->options;
+        struct fat_mount_options *options = &MSDOS_SB(parent->d_sb)->options;
         unsigned char a_msdos_name[MSDOS_NAME], b_msdos_name[MSDOS_NAME];
         int error;
 
-        error = msdos_format_name(a->name, a->len, a_msdos_name, options);
+        error = msdos_format_name(name->name, name->len, a_msdos_name, options);
         if (error)
                 goto old_compare;
-        error = msdos_format_name(b->name, b->len, b_msdos_name, options);
+        error = msdos_format_name(str, len, b_msdos_name, options);
         if (error)
                 goto old_compare;
         error = memcmp(a_msdos_name, b_msdos_name, MSDOS_NAME);
@@ -182,8 +184,8 @@ out:
 
 old_compare:
         error = 1;
-        if (a->len == b->len)
-                error = memcmp(a->name, b->name, a->len);
+        if (name->len == len)
+                error = memcmp(name->name, str, len);
         goto out;
 }