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Subject[PATCH 1/6 v6] vfs: add i_op->open()
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>
---
fs/open.c | 83 +++++++++++++++++++++++++++++++----------------------
include/linux/fs.h | 2 +
2 files changed, 51 insertions(+), 34 deletions(-)

Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h 2011-03-01 12:18:10.000000000 +0100
+++ linux-2.6/include/linux/fs.h 2011-03-01 12:18:15.000000000 +0100
@@ -1587,6 +1587,7 @@ 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 *, int flags, const struct cred *);
} ____cacheline_aligned;

struct seq_file;
@@ -1990,6 +1991,7 @@ extern int do_fallocate(struct file *fil
extern long do_sys_open(int dfd, const char __user *filename, int flags,
int mode);
extern struct file *filp_open(const char *, int, int);
+extern struct file *vfs_open(struct path *, int flags, 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);
Index: linux-2.6/fs/open.c
===================================================================
--- linux-2.6.orig/fs/open.c 2011-03-01 12:18:10.000000000 +0100
+++ linux-2.6/fs/open.c 2011-03-01 12:18:15.000000000 +0100
@@ -656,19 +656,19 @@ static inline int __get_file_write_acces
return error;
}

-static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
- struct file *f,
+static struct file *__dentry_open(struct path *path, struct file *f,
int (*open)(struct inode *, struct file *),
const struct cred *cred)
{
struct inode *inode;
int error;

+ path_get(path);
f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
FMODE_PREAD | FMODE_PWRITE;
- inode = dentry->d_inode;
+ inode = path->dentry->d_inode;
if (f->f_mode & FMODE_WRITE) {
- error = __get_file_write_access(inode, mnt);
+ error = __get_file_write_access(inode, path->mnt);
if (error)
goto cleanup_file;
if (!special_file(inode->i_mode))
@@ -676,8 +676,7 @@ static struct file *__dentry_open(struct
}

f->f_mapping = inode->i_mapping;
- f->f_path.dentry = dentry;
- f->f_path.mnt = mnt;
+ f->f_path = *path;
f->f_pos = 0;
f->f_op = fops_get(inode->i_fop);
file_sb_list_add(f, inode->i_sb);
@@ -723,7 +722,7 @@ static struct file *__dentry_open(struct
* here, so just reset the state.
*/
file_reset_write(f);
- mnt_drop_write(mnt);
+ mnt_drop_write(path->mnt);
}
}
file_sb_list_del(f);
@@ -731,8 +730,7 @@ static struct file *__dentry_open(struct
f->f_path.mnt = NULL;
cleanup_file:
put_filp(f);
- dput(dentry);
- mntput(mnt);
+ path_put(path);
return ERR_PTR(error);
}

@@ -758,14 +756,14 @@ static struct file *__dentry_open(struct
struct file *lookup_instantiate_filp(struct nameidata *nd, struct dentry *dentry,
int (*open)(struct inode *, struct file *))
{
+ struct path path = { .dentry = dentry, .mnt = nd->path.mnt };
const struct cred *cred = current_cred();

if (IS_ERR(nd->intent.open.file))
goto out;
if (IS_ERR(dentry))
goto out_err;
- nd->intent.open.file = __dentry_open(dget(dentry), mntget(nd->path.mnt),
- nd->intent.open.file,
+ nd->intent.open.file = __dentry_open(&path, nd->intent.open.file,
open, cred);
out:
return nd->intent.open.file;
@@ -794,10 +792,17 @@ struct file *nameidata_to_filp(struct na

/* Has the filesystem initialised the file for us? */
if (filp->f_path.dentry == NULL) {
- path_get(&nd->path);
- filp = __dentry_open(nd->path.dentry, nd->path.mnt, filp,
- NULL, cred);
+ struct inode *inode = nd->path.dentry->d_inode;
+
+ if (inode->i_op->open) {
+ int flags = filp->f_flags;
+ put_filp(filp);
+ filp = inode->i_op->open(nd->path.dentry, flags, cred);
+ } else {
+ filp = __dentry_open(&nd->path, filp, NULL, cred);
+ }
}
+
return filp;
}

@@ -808,35 +813,45 @@ struct file *nameidata_to_filp(struct na
struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags,
const struct cred *cred)
{
- int error;
+ struct path path = { .dentry = dentry, .mnt = mnt };
+ struct file *ret;
+
+ BUG_ON(!mnt);
+
+ ret = vfs_open(&path, flags, cred);
+ path_put(&path);
+
+ return ret;
+}
+EXPORT_SYMBOL(dentry_open);
+
+/**
+ * vfs_open - open the file at the given path
+ * @path: path to open
+ * @flags: open flags
+ * @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, int flags, const struct cred *cred)
+{
struct file *f;
+ struct inode *inode = path->dentry->d_inode;

validate_creds(cred);

- /*
- * We must always pass in a valid mount pointer. Historically
- * callers got away with not passing it, but we must enforce this at
- * the earliest possible point now to avoid strange problems deep in the
- * filesystem stack.
- */
- if (!mnt) {
- printk(KERN_WARNING "%s called with NULL vfsmount\n", __func__);
- dump_stack();
- return ERR_PTR(-EINVAL);
- }
+ if (inode->i_op->open)
+ return inode->i_op->open(path->dentry, flags, cred);

- error = -ENFILE;
f = get_empty_filp();
- if (f == NULL) {
- dput(dentry);
- mntput(mnt);
- return ERR_PTR(error);
- }
+ if (f == NULL)
+ return ERR_PTR(-ENFILE);

f->f_flags = flags;
- return __dentry_open(dentry, mnt, f, NULL, cred);
+ return __dentry_open(path, f, NULL, cred);
}
-EXPORT_SYMBOL(dentry_open);
+EXPORT_SYMBOL(vfs_open);

static void __put_unused_fd(struct files_struct *files, unsigned int fd)
{
--


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