[PATCH v2 1/2] tmpfs: manage the inode-number by IDR

["J. R. Okajima" <hooanon05g@gmail.com>]

To ensure the uniquness of the inode-number, manage it by IDR.
Also it tries using the lowest unused inode-number, so the value will
usually be smaller.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andreas Dilger <adilger@dilger.ca>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
---
 include/linux/shmem_fs.h |    2 ++
 mm/shmem.c               |   20 +++++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 4d1771c..30c75f0 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -24,6 +24,8 @@ struct shmem_inode_info {
 };
 
 struct shmem_sb_info {
+	struct mutex idr_lock;
+	struct idr idr;		    /* manages inode-number */
 	unsigned long max_blocks;   /* How many blocks are allowed */
 	struct percpu_counter used_blocks;  /* How many are allocated */
 	unsigned long max_inodes;   /* How many inodes are allowed */
diff --git a/mm/shmem.c b/mm/shmem.c
index 368f314..440db70 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -569,6 +569,7 @@ static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
 static void shmem_evict_inode(struct inode *inode)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
+	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 
 	if (inode->i_mapping->a_ops == &shmem_aops) {
 		shmem_unacct_size(info->flags, inode->i_size);
@@ -584,6 +585,9 @@ static void shmem_evict_inode(struct inode *inode)
 
 	simple_xattrs_free(&info->xattrs);
 	WARN_ON(inode->i_blocks);
+	mutex_lock(&sbinfo->idr_lock);
+	idr_remove(&sbinfo->idr, inode->i_ino);
+	mutex_unlock(&sbinfo->idr_lock);
 	shmem_free_inode(inode->i_sb);
 	clear_inode(inode);
 }
@@ -1315,13 +1319,13 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 	struct inode *inode;
 	struct shmem_inode_info *info;
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
+	long long ino; /* signed to detect an error */
 
 	if (shmem_reserve_inode(sb))
 		return NULL;
 
 	inode = new_inode(sb);
 	if (inode) {
-		inode->i_ino = get_next_ino();
 		inode_init_owner(inode, dir, mode);
 		inode->i_blocks = 0;
 		inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
@@ -1362,6 +1366,17 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 			mpol_shared_policy_init(&info->policy, NULL);
 			break;
 		}
+
+		/* inum 0 and 1 are unused */
+		mutex_lock(&sbinfo->idr_lock);
+		ino = idr_alloc(&sbinfo->idr, inode, 2, UINT_MAX, GFP_NOFS);
+		if (ino > 0)
+			inode->i_ino = ino;
+		mutex_unlock(&sbinfo->idr_lock);
+		if (unlikely(ino < 0)) {
+			iput(inode);	/* shmem_free_inode() will be called */
+			inode = NULL;
+		}
 	} else
 		shmem_free_inode(sb);
 	return inode;
@@ -2504,6 +2519,7 @@ static void shmem_put_super(struct super_block *sb)
 {
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
 
+	idr_destroy(&sbinfo->idr);
 	percpu_counter_destroy(&sbinfo->used_blocks);
 	mpol_put(sbinfo->mpol);
 	kfree(sbinfo);
@@ -2522,6 +2538,8 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
 	if (!sbinfo)
 		return -ENOMEM;
 
+	mutex_init(&sbinfo->idr_lock);
+	idr_init(&sbinfo->idr);
 	sbinfo->mode = S_IRWXUGO | S_ISVTX;
 	sbinfo->uid = current_fsuid();
 	sbinfo->gid = current_fsgid();
-- 
1.7.10.4