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From: Valerie Aurora on 8 Aug 2010 12:00
Add support for fallthru directory entries to tmpfs

Signed-off-by: Valerie Aurora <vaurora(a)redhat.com>
---
fs/dcache.c | 3 +-
fs/libfs.c | 23 ++++++++++++++++++--
mm/shmem.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
3 files changed, 78 insertions(+), 12 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index ed7f15a..4fe51a9 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2254,7 +2254,8 @@ resume:
* we can evict it.
*/
if (d_unhashed(dentry)||(!dentry->d_inode &&
- !d_is_whiteout(dentry)))
+ !d_is_whiteout(dentry) &&
+ !d_is_fallthru(dentry)))
continue;
if (!list_empty(&dentry->d_subdirs)) {
this_parent = dentry;
diff --git a/fs/libfs.c b/fs/libfs.c
index dcaf972..1172f1a 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -130,6 +130,7 @@ int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir)
struct dentry *cursor = filp->private_data;
struct list_head *p, *q = &cursor->d_u.d_child;
ino_t ino;
+ char d_type;
int i = filp->f_pos;

switch (i) {
@@ -155,14 +156,30 @@ int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir)
for (p=q->next; p != &dentry->d_subdirs; p=p->next) {
struct dentry *next;
next = list_entry(p, struct dentry, d_u.d_child);
- if (d_unhashed(next) || !next->d_inode)
+ if (d_unhashed(next) || (!next->d_inode && !d_is_fallthru(next)))
continue;

spin_unlock(&dcache_lock);
+ if (d_is_fallthru(next)) {
+ /*
+ * Fallthru lookup should never fail on tmpfs (except
+ * ENOMEM and the like). If fallthru fails, better to
+ * fake up return values than crash.
+ */
+ ino = 1;
+ d_type = DT_UNKNOWN;
+ generic_readdir_fallthru(filp->f_path.dentry,
+ next->d_name.name,
+ next->d_name.len,
+ &ino, &d_type);
+ } else {
+ ino = next->d_inode->i_ino;
+ d_type = dt_type(next->d_inode);
+ }
+
if (filldir(dirent, next->d_name.name,
next->d_name.len, filp->f_pos,
- next->d_inode->i_ino,
- dt_type(next->d_inode)) < 0)
+ ino, d_type) < 0)
return 0;
spin_lock(&dcache_lock);
/* next is still alive */
diff --git a/mm/shmem.c b/mm/shmem.c
index a0a4fa5..eab3f27 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1809,8 +1809,7 @@ static int shmem_rmdir(struct inode *dir, struct dentry *dentry);
static int shmem_unlink(struct inode *dir, struct dentry *dentry);

/*
- * This is the whiteout support for tmpfs. It uses one singleton whiteout
- * inode per superblock thus it is very similar to shmem_link().
+ * Create a dentry to signify a whiteout.
*/
static int shmem_whiteout(struct inode *dir, struct dentry *old_dentry,
struct dentry *new_dentry)
@@ -1841,8 +1840,10 @@ static int shmem_whiteout(struct inode *dir, struct dentry *old_dentry,
spin_unlock(&sbinfo->stat_lock);
}

- if (old_dentry->d_inode) {
- if (S_ISDIR(old_dentry->d_inode->i_mode))
+ if (old_dentry->d_inode || d_is_fallthru(old_dentry)) {
+ /* A fallthru for a dir is treated like a regular link */
+ if (old_dentry->d_inode &&
+ S_ISDIR(old_dentry->d_inode->i_mode))
shmem_rmdir(dir, old_dentry);
else
shmem_unlink(dir, old_dentry);
@@ -1859,6 +1860,48 @@ static int shmem_whiteout(struct inode *dir, struct dentry *old_dentry,
}

static void shmem_d_instantiate(struct inode *dir, struct dentry *dentry,
+ struct inode *inode);
+
+/*
+ * Create a dentry to signify a fallthru. A fallthru in tmpfs is the
+ * logical equivalent of an in-kernel readdir() cache. It can't be
+ * deleted until the file system is unmounted.
+ */
+static int shmem_fallthru(struct inode *dir, struct dentry *dentry)
+{
+ struct shmem_sb_info *sbinfo = SHMEM_SB(dir->i_sb);
+
+ /* FIXME: this is stupid */
+ if (!(dir->i_sb->s_flags & MS_WHITEOUT))
+ return -EPERM;
+
+ if (dentry->d_inode || d_is_fallthru(dentry) || d_is_whiteout(dentry))
+ return -EEXIST;
+
+ /*
+ * Each new link needs a new dentry, pinning lowmem, and tmpfs
+ * dentries cannot be pruned until they are unlinked.
+ */
+ if (sbinfo->max_inodes) {
+ spin_lock(&sbinfo->stat_lock);
+ if (!sbinfo->free_inodes) {
+ spin_unlock(&sbinfo->stat_lock);
+ return -ENOSPC;
+ }
+ sbinfo->free_inodes--;
+ spin_unlock(&sbinfo->stat_lock);
+ }
+
+ shmem_d_instantiate(dir, dentry, NULL);
+ dir->i_ctime = dir->i_mtime = CURRENT_TIME;
+
+ spin_lock(&dentry->d_lock);
+ dentry->d_flags |= DCACHE_FALLTHRU;
+ spin_unlock(&dentry->d_lock);
+ return 0;
+}
+
+static void shmem_d_instantiate(struct inode *dir, struct dentry *dentry,
struct inode *inode)
{
if (d_is_whiteout(dentry)) {
@@ -1866,14 +1909,15 @@ static void shmem_d_instantiate(struct inode *dir, struct dentry *dentry,
shmem_free_inode(dir->i_sb);
if (S_ISDIR(inode->i_mode))
inode->i_mode |= S_OPAQUE;
+ } else if (d_is_fallthru(dentry)) {
+ shmem_free_inode(dir->i_sb);
} else {
/* New dentry */
dir->i_size += BOGO_DIRENT_SIZE;
dget(dentry); /* Extra count - pin the dentry in core */
}
- /* Will clear DCACHE_WHITEOUT flag */
+ /* Will clear DCACHE_WHITEOUT and DCACHE_FALLTHRU flags */
d_instantiate(dentry, inode);
-
}
/*
* File creation. Allocate an inode, and we're done..
@@ -1955,7 +1999,8 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry)
{
struct inode *inode = dentry->d_inode;

- if (d_is_whiteout(dentry) || (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode)))
+ if (d_is_whiteout(dentry) || d_is_fallthru(dentry) ||
+ (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode)))
shmem_free_inode(dir->i_sb);

if (inode) {
@@ -2479,8 +2524,10 @@ int shmem_fill_super(struct super_block *sb, void *data, int silent)
sb->s_root = root;

#ifdef CONFIG_TMPFS
- if (!(sb->s_flags & MS_NOUSER))
+ if (!(sb->s_flags & MS_NOUSER)) {
sb->s_flags |= MS_WHITEOUT;
+ sb->s_flags |= MS_FALLTHRU;
+ }
#endif

return 0;
@@ -2583,6 +2630,7 @@ static const struct inode_operations shmem_dir_inode_operations = {
.mknod = shmem_mknod,
.rename = shmem_rename,
.whiteout = shmem_whiteout,
+ .fallthru = shmem_fallthru,
#endif
#ifdef CONFIG_TMPFS_POSIX_ACL
.setattr = shmem_notify_change,
--
1.6.3.3

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Prev: [PATCH 03/39] VFS: Add read-only users count to superblock
Next: [PATCH 15/39] union-mount: Introduce MNT_UNION and MS_UNION flags