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Date: Wed, 21 Dec 2011 19:29:41 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: viro@...IV.linux.org.uk, torvalds@...ux-foundation.org
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
hch@...radead.org, akpm@...ux-foundation.org, apw@...onical.com,
nbd@...nwrt.org, neilb@...e.de, hramrach@...trum.cz,
jordipujolp@...il.com, ezk@....cs.sunysb.edu, ricwheeler@...il.com,
dhowells@...hat.com, hpj@...la.net, sedat.dilek@...glemail.com,
penberg@...nel.org, mszeredi@...e.cz
Subject: [PATCH 2/9] vfs: add i_op->open()
From: Miklos Szeredi <mszeredi@...e.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@...e.cz>
---
Documentation/filesystems/Locking | 2 ++
Documentation/filesystems/vfs.txt | 8 ++++++++
fs/open.c | 25 +++++++++++++++++++++++--
include/linux/fs.h | 3 +++
4 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 4fca82e..42b0539 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -62,6 +62,7 @@ ata *);
int (*removexattr) (struct dentry *, const char *);
void (*truncate_range)(struct inode *, loff_t, loff_t);
int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
+ struct file *(*open)(struct dentry *,struct file *,const struct cred *);
locking rules:
all may block
@@ -89,6 +90,7 @@ listxattr: no
removexattr: yes
truncate_range: yes
fiemap: no
+open: no
Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
victim.
cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 3d9393b..3c65a0f 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -364,6 +364,8 @@ struct inode_operations {
ssize_t (*listxattr) (struct dentry *, char *, size_t);
int (*removexattr) (struct dentry *, const char *);
void (*truncate_range)(struct inode *, loff_t, loff_t);
+ struct file *(*open) (struct dentry *, struct file *,
+ const struct cred *);
};
Again, all methods are called without any locks being held, unless
@@ -475,6 +477,12 @@ otherwise noted.
truncate_range: a method provided by the underlying filesystem to truncate a
range of blocks , i.e. punch a hole somewhere in a file.
+ open: this is an alternative to f_op->open(), the difference is that this
+ method may return any open 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.
+
The Address Space Object
========================
diff --git a/fs/open.c b/fs/open.c
index ceab906..7f56fc1 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -796,7 +796,7 @@ struct file *nameidata_to_filp(struct nameidata *nd)
/* Has the filesystem initialised the file for us? */
if (filp->f_path.dentry == NULL)
- filp = __dentry_open(&nd->path, filp, NULL, cred);
+ filp = vfs_open(&nd->path, filp, cred);
return filp;
}
@@ -821,7 +821,7 @@ struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags,
f = get_empty_filp();
if (f != NULL) {
f->f_flags = flags;
- ret = __dentry_open(&path, f, NULL, cred);
+ ret = vfs_open(&path, f, cred);
}
path_put(&path);
@@ -829,6 +829,27 @@ struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, 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
+ *
+ * Open the file. If successful, the returned file will have acquired
+ * an additional reference for path.
+ */
+struct file *vfs_open(struct path *path, struct file *filp,
+ const struct cred *cred)
+{
+ struct inode *inode = path->dentry->d_inode;
+
+ if (inode->i_op->open)
+ return inode->i_op->open(path->dentry, filp, cred);
+ else
+ return __dentry_open(path, 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 df499ad..c744032 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1645,6 +1645,8 @@ struct inode_operations {
void (*truncate_range)(struct inode *, loff_t, loff_t);
int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
u64 len);
+ struct file *(*open) (struct dentry *, struct file *,
+ const struct cred *);
} ____cacheline_aligned;
struct seq_file;
@@ -2015,6 +2017,7 @@ 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 struct file *vfs_open(struct path *, struct file *, const struct cred *);
extern struct file * dentry_open(struct dentry *, struct vfsmount *, int,
const struct cred *);
extern int filp_close(struct file *, fl_owner_t id);
--
1.7.7
--
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