fat: Fix/Cleanup dcache handling for vfat

- Add comments for handling dcache of vfat.

- Separate case-sensitive case and case-insensitive to
  vfat_revalidate() and vfat_ci_revalidate().

  vfat_revalidate() doesn't need to drop case-insensitive negative
  dentry on creation path.

- Current code is missing to set ->d_revalidate to the negative dentry
  created by unlink/etc..

  This sets ->d_revalidate always, and returns 1 for positive
  dentry. Now, we don't need to change ->d_op dynamically anymore,
  so this just uses sb->s_root->d_op to set ->d_op.

- d_find_alias() may return DCACHE_DISCONNECTED dentry. It's not
  the interesting dentry there. This checks it.

- Add missing LOOKUP_PARENT check. We don't need to drop the valid
  negative dentry for (LOOKUP_CREATE | LOOKUP_PARENT) lookup.

- For consistent filename on creation path, this drops negative dentry
  if we can't see intent.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 80 insertions, 44 deletions

diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 419deabfb9be..d585398f9f6b 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -24,27 +24,67 @@
 #include <linux/namei.h>
 #include "fat.h"
 
-static int vfat_revalidate(struct dentry *dentry, struct nameidata *nd)
+/*
+ * If new entry was created in the parent, it could create the 8.3
+ * alias (the shortname of logname).  So, the parent may have the
+ * negative-dentry which matches the created 8.3 alias.
+ *
+ * If it happened, the negative dentry isn't actually negative
+ * anymore.  So, drop it.
+ */
+static int vfat_revalidate_shortname(struct dentry *dentry)
 {
         int ret = 1;
-
-        if (!dentry->d_inode &&
-            nd && !(nd->flags & LOOKUP_CONTINUE) && (nd->flags & LOOKUP_CREATE))
-                /*
-                 * negative dentry is dropped, in order to make sure
-                 * to use the name which a user desires if this is
-                 * create path.
-                 */
+        spin_lock(&dentry->d_lock);
+        if (dentry->d_time != dentry->d_parent->d_inode->i_version)
                 ret = 0;
-        else {
-                spin_lock(&dentry->d_lock);
-                if (dentry->d_time != dentry->d_parent->d_inode->i_version)
-                        ret = 0;
-                spin_unlock(&dentry->d_lock);
-        }
+        spin_unlock(&dentry->d_lock);
         return ret;
 }
 
+static int vfat_revalidate(struct dentry *dentry, struct nameidata *nd)
+{
+        /* This is not negative dentry. Always valid. */
+        if (dentry->d_inode)
+                return 1;
+        return vfat_revalidate_shortname(dentry);
+}
+
+static int vfat_revalidate_ci(struct dentry *dentry, struct nameidata *nd)
+{
+        /*
+         * This is not negative dentry. Always valid.
+         *
+         * Note, rename() to existing directory entry will have ->d_inode,
+         * and will use existing name which isn't specified name by user.
+         *
+         * We may be able to drop this positive dentry here. But dropping
+         * positive dentry isn't good idea. So it's unsupported like
+         * rename("filename", "FILENAME") for now.
+         */
+        if (dentry->d_inode)
+                return 1;
+
+        /*
+         * This may be nfsd (or something), anyway, we can't see the
+         * intent of this. So, since this can be for creation, drop it.
+         */
+        if (!nd)
+                return 0;
+
+        /*
+         * Drop the negative dentry, in order to make sure to use the
+         * case sensitive name which is specified by user if this is
+         * for creation.
+         */
+        if (!(nd->flags & (LOOKUP_CONTINUE | LOOKUP_PARENT))) {
+                if (nd->flags & LOOKUP_CREATE)
+                        return 0;
+        }
+
+        return vfat_revalidate_shortname(dentry);
+}
+
 /* returns the length of a struct qstr, ignoring trailing dots */
 static unsigned int vfat_striptail_len(struct qstr *qstr)
 {
@@ -126,25 +166,16 @@ static int vfat_cmp(struct dentry *dentry, struct qstr *a, struct qstr *b)
         return 1;
 }
 
-static struct dentry_operations vfat_dentry_ops[4] = {
-        {
-                .d_hash         = vfat_hashi,
-                .d_compare      = vfat_cmpi,
-        },
-        {
-                .d_revalidate   = vfat_revalidate,
-                .d_hash         = vfat_hashi,
-                .d_compare      = vfat_cmpi,
-        },
-        {
-                .d_hash         = vfat_hash,
-                .d_compare      = vfat_cmp,
-        },
-        {
-                .d_revalidate   = vfat_revalidate,
-                .d_hash         = vfat_hash,
-                .d_compare      = vfat_cmp,
-        }
+static struct dentry_operations vfat_ci_dentry_ops = {
+        .d_revalidate   = vfat_revalidate_ci,
+        .d_hash         = vfat_hashi,
+        .d_compare      = vfat_cmpi,
+};
+
+static struct dentry_operations vfat_dentry_ops = {
+        .d_revalidate   = vfat_revalidate,
+        .d_hash         = vfat_hash,
+        .d_compare      = vfat_cmp,
 };
 
 /* Characters that are undesirable in an MS-DOS file name */
@@ -685,29 +716,35 @@ static struct dentry *vfat_lookup(struct inode *dir, struct dentry *dentry,
         struct fat_slot_info sinfo;
         struct inode *inode;
         struct dentry *alias;
-        int err, table;
+        int err;
 
         lock_super(sb);
-        table = (MSDOS_SB(sb)->options.name_check == 's') ? 2 : 0;
-        dentry->d_op = &vfat_dentry_ops[table];
 
         err = vfat_find(dir, &dentry->d_name, &sinfo);
         if (err) {
                 if (err == -ENOENT) {
-                        table++;
                         inode = NULL;
                         goto out;
                 }
                 goto error;
         }
+
         inode = fat_build_inode(sb, sinfo.de, sinfo.i_pos);
         brelse(sinfo.bh);
         if (IS_ERR(inode)) {
                 err = PTR_ERR(inode);
                 goto error;
         }
+
         alias = d_find_alias(inode);
-        if (alias) {
+        if (alias && !(alias->d_flags & DCACHE_DISCONNECTED)) {
+                /*
+                 * This inode has non DCACHE_DISCONNECTED dentry. This
+                 * means, the user did ->lookup() by an another name
+                 * (longname vs 8.3 alias of it) in past.
+                 *
+                 * Switch to new one for reason of locality if possible.
+                 */
                 if (d_invalidate(alias) == 0)
                         dput(alias);
                 else {
@@ -715,15 +752,14 @@ static struct dentry *vfat_lookup(struct inode *dir, struct dentry *dentry,
                         unlock_super(sb);
                         return alias;
                 }
-
         }
 out:
         unlock_super(sb);
-        dentry->d_op = &vfat_dentry_ops[table];
+        dentry->d_op = sb->s_root->d_op;
         dentry->d_time = dentry->d_parent->d_inode->i_version;
         dentry = d_splice_alias(inode, dentry);
         if (dentry) {
-                dentry->d_op = &vfat_dentry_ops[table];
+                dentry->d_op = sb->s_root->d_op;
                 dentry->d_time = dentry->d_parent->d_inode->i_version;
         }
         return dentry;
@@ -1022,9 +1058,9 @@ static int vfat_fill_super(struct super_block *sb, void *data, int silent)
                 return res;
 
         if (MSDOS_SB(sb)->options.name_check != 's')
-                sb->s_root->d_op = &vfat_dentry_ops[0];
+                sb->s_root->d_op = &vfat_ci_dentry_ops;
         else
-                sb->s_root->d_op = &vfat_dentry_ops[2];
+                sb->s_root->d_op = &vfat_dentry_ops;
 
         return 0;
 }