[PATCH 01/13] vfs: add i_op->open()

Miklos Szeredi
2012-08-15T15:50:53Z

From: Miklos Szeredi <mszeredi@suse.cz>

Add a new inode operation i_op->open(). This is for stacked
filesystems that want to return a struct file from a different
filesystem.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
Documentation/filesystems/Locking | 2 ++
Documentation/filesystems/vfs.txt | 7 +++++++
fs/namei.c | 9 ++++++---
fs/open.c | 23 +++++++++++++++++++++--
include/linux/fs.h | 2 ++
5 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 0f103e3..d222b6a 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -64,6 +64,7 @@ prototypes:
int (*atomic_open)(struct inode *, struct dentry *,
struct file *, unsigned open_flag,
umode_t create_mode, int *opened);
+ int (*dentry_open)(struct dentry *, struct file *, const struct cred *);

locking rules:
all may block
@@ -92,6 +93,7 @@ removexattr: yes
fiemap: no
update_time: no
atomic_open: yes
+open: no

Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
victim.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 065aa2d..f53d93c 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -367,6 +367,7 @@ struct inode_operations {
int (*atomic_open)(struct inode *, struct dentry *,
struct file *, unsigned open_flag,
umode_t create_mode, int *opened);
+ int (*dentry_open)(struct dentry *, struct file *, const struct cred *);
};

Again, all methods are called without any locks being held, unless
@@ -696,6 +697,12 @@ struct address_space_operations {
but instead uses bmap to find out where the blocks in the file
are and uses those addresses directly.

+ dentry_open: this is an alternative to f_op->open(), the difference is that
+ this method may open a file not necessarily originating from the same
+ filesystem as the one i_op->open() was called on. It may be
+ useful for stacking filesystems which want to allow native I/O directly
+ on underlying files.
+

invalidatepage: If a page has PagePrivate set, then invalidatepage
will be called when part or all of the page is to be removed
diff --git a/fs/namei.c b/fs/namei.c
index 1b46439..ac2526d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2816,9 +2816,12 @@ finish_open_created:
error = may_open(&nd->path, acc_mode, open_flag);
if (error)
goto out;
- file->f_path.mnt = nd->path.mnt;
- error = finish_open(file, nd->path.dentry, NULL, opened);
- if (error) {
+
+ BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
+ error = vfs_open(&nd->path, file, current_cred());
+ if (!error) {
+ *opened |= FILE_OPENED;
+ } else {
if (error == -EOPENSTALE)
goto stale_open;
goto out;
diff --git a/fs/open.c b/fs/open.c
index f3d96e7..c5a8cac 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -787,8 +787,7 @@ struct file *dentry_open(const struct path *path, int flags,
return ERR_PTR(error);

f->f_flags = flags;
- f->f_path = *path;
- error = do_dentry_open(f, NULL, cred);
+ error = vfs_open(path, f, cred);
if (!error) {
error = open_check_o_direct(f);
if (error) {
@@ -803,6 +802,26 @@ struct file *dentry_open(const struct path *path, int flags,
}
EXPORT_SYMBOL(dentry_open);

+/**
+ * vfs_open - open the file at the given path
+ * @path: path to open
+ * @filp: newly allocated file with f_flag initialized
+ * @cred: credentials to use
+ */
+int vfs_open(const struct path *path, struct file *filp,
+ const struct cred *cred)
+{
+ struct inode *inode = path->dentry->d_inode;
+
+ if (inode->i_op->dentry_open)
+ return inode->i_op->dentry_open(path->dentry, filp, cred);
+ else {
+ filp->f_path = *path;
+ return do_dentry_open(filp, NULL, cred);
+ }
+}
+EXPORT_SYMBOL(vfs_open);
+
static void __put_unused_fd(struct files_struct *files, unsigned int fd)
{
struct fdtable *fdt = files_fdtable(files);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 38dba16..abc7a53 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1836,6 +1836,7 @@ struct inode_operations {
int (*atomic_open)(struct inode *, struct dentry *,
struct file *, unsigned open_flag,
umode_t create_mode, int *opened);
+ int (*dentry_open)(struct dentry *, struct file *, const struct cred *);
} ____cacheline_aligned;

struct seq_file;
@@ -2201,6 +2202,7 @@ extern long do_sys_open(int dfd, const char __user *filename, int flags,
extern struct file *filp_open(const char *, int, umode_t);
extern struct file *file_open_root(struct dentry *, struct vfsmount *,
const char *, int);
+extern int vfs_open(const struct path *, struct file *, const struct cred *);
extern struct file * dentry_open(const struct path *, int, const struct cred *);
extern int filp_close(struct file *, fl_owner_t id);
extern char * getname(const char __user *);
--
1.7.7