quota: Introduce DQUOT_QUOTA_SYS_FILE flag

If filesystem can handle quota files as system files hidden from users, we can
skip a lot of cache invalidation, syncing, inode flags setting etc. when
turning quotas on, off and quota_sync. Allow filesystem to indicate that it is
hiding quota files from users by DQUOT_QUOTA_SYS_FILE flag.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

3 files changed, 40 insertions, 15 deletions

diff --git a/fs/dquot.c b/fs/dquot.c
index 7569633efe0e..74185c34a4f0 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -1631,6 +1631,11 @@ int vfs_quota_disable(struct super_block *sb, int type, unsigned int flags)
                 dqopt->ops[cnt] = NULL;
         }
         mutex_unlock(&dqopt->dqonoff_mutex);
+
+        /* Skip syncing and setting flags if quota files are hidden */
+        if (dqopt->flags & DQUOT_QUOTA_SYS_FILE)
+                goto put_inodes;
+
         /* Sync the superblock so that buffers with quota data are written to
          * disk (and so userspace sees correct data afterwards). */
         if (sb->s_op->sync_fs)
@@ -1655,6 +1660,12 @@ int vfs_quota_disable(struct super_block *sb, int type, unsigned int flags)
                                 mark_inode_dirty(toputinode[cnt]);
                         }
                         mutex_unlock(&dqopt->dqonoff_mutex);
+                }
+        if (sb->s_bdev)
+                invalidate_bdev(sb->s_bdev);
+put_inodes:
+        for (cnt = 0; cnt < MAXQUOTAS; cnt++)
+                if (toputinode[cnt]) {
                         /* On remount RO, we keep the inode pointer so that we
                          * can reenable quota on the subsequent remount RW. We
                          * have to check 'flags' variable and not use sb_has_
@@ -1667,8 +1678,6 @@ int vfs_quota_disable(struct super_block *sb, int type, unsigned int flags)
                         else if (!toputinode[cnt]->i_nlink)
                                 ret = -EBUSY;
                 }
-        if (sb->s_bdev)
-                invalidate_bdev(sb->s_bdev);
         return ret;
 }
 
@@ -1715,25 +1724,31 @@ static int vfs_load_quota_inode(struct inode *inode, int type, int format_id,
                 goto out_fmt;
         }
 
-        /* As we bypass the pagecache we must now flush the inode so that
-         * we see all the changes from userspace... */
-        write_inode_now(inode, 1);
-        /* And now flush the block cache so that kernel sees the changes */
-        invalidate_bdev(sb->s_bdev);
+        if (!(dqopt->flags & DQUOT_QUOTA_SYS_FILE)) {
+                /* As we bypass the pagecache we must now flush the inode so
+                 * that we see all the changes from userspace... */
+                write_inode_now(inode, 1);
+                /* And now flush the block cache so that kernel sees the
+                 * changes */
+                invalidate_bdev(sb->s_bdev);
+        }
         mutex_lock(&inode->i_mutex);
         mutex_lock(&dqopt->dqonoff_mutex);
         if (sb_has_quota_loaded(sb, type)) {
                 error = -EBUSY;
                 goto out_lock;
         }
-        /* We don't want quota and atime on quota files (deadlocks possible)
-         * Also nobody should write to the file - we use special IO operations
-         * which ignore the immutable bit. */
-        down_write(&dqopt->dqptr_sem);
-        oldflags = inode->i_flags & (S_NOATIME | S_IMMUTABLE | S_NOQUOTA);
-        inode->i_flags |= S_NOQUOTA | S_NOATIME | S_IMMUTABLE;
-        up_write(&dqopt->dqptr_sem);
-        sb->dq_op->drop(inode);
+
+        if (!(dqopt->flags & DQUOT_QUOTA_SYS_FILE)) {
+                /* We don't want quota and atime on quota files (deadlocks
+                 * possible) Also nobody should write to the file - we use
+                 * special IO operations which ignore the immutable bit. */
+                down_write(&dqopt->dqptr_sem);
+                oldflags = inode->i_flags & (S_NOATIME | S_IMMUTABLE | S_NOQUOTA);
+                inode->i_flags |= S_NOQUOTA | S_NOATIME | S_IMMUTABLE;
+                up_write(&dqopt->dqptr_sem);
+                sb->dq_op->drop(inode);
+        }
 
         error = -EIO;
         dqopt->files[type] = igrab(inode);
diff --git a/fs/quota.c b/fs/quota.c
index 8678d9f35ee9..4a8c94f05f76 100644
--- a/fs/quota.c
+++ b/fs/quota.c
@@ -160,6 +160,9 @@ static void quota_sync_sb(struct super_block *sb, int type)
         int cnt;
 
         sb->s_qcop->quota_sync(sb, type);
+
+        if (sb_dqopt(sb)->flags & DQUOT_QUOTA_SYS_FILE)
+                return;
         /* This is not very clever (and fast) but currently I don't know about
          * any other simple way of getting quota data to disk and we must get
          * them there for userspace to be visible... */
diff --git a/include/linux/quota.h b/include/linux/quota.h
index 93717abcd35b..80b8807b4988 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -332,6 +332,13 @@ enum {
 #define DQUOT_SUSPENDED         (1 << _DQUOT_SUSPENDED)
 #define DQUOT_STATE_FLAGS       (DQUOT_USAGE_ENABLED | DQUOT_LIMITS_ENABLED | \
                                  DQUOT_SUSPENDED)
+/* Other quota flags */
+#define DQUOT_QUOTA_SYS_FILE    (1 << 6)        /* Quota file is a special
+                                                 * system file and user cannot
+                                                 * touch it. Filesystem is
+                                                 * responsible for setting
+                                                 * S_NOQUOTA, S_NOATIME flags
+                                                 */
 
 static inline unsigned int dquot_state_flag(unsigned int flags, int type)
 {