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Subject[PATCH 2/7] vfs: add i_op->open()
Date
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 | 76 ++++++++++++++++++++++++++++++++++------------------
include/linux/fs.h | 2 +
2 files changed, 52 insertions(+), 26 deletions(-)
diff --git a/fs/open.c b/fs/open.c
index b52cf01..84fa16a 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -666,8 +666,7 @@ static inline int __get_file_write_access(struct inode *inode,
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)
{
@@ -675,15 +674,16 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
struct inode *inode;
int error;

+ path_get(path);
f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
FMODE_PREAD | FMODE_PWRITE;

if (unlikely(f->f_flags & O_PATH))
f->f_mode = FMODE_PATH;

- 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))
@@ -691,8 +691,7 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
}

f->f_mapping = inode->i_mapping;
- f->f_path.dentry = dentry;
- f->f_path.mnt = mnt;
+ f->f_path = *path;
f->f_pos = 0;
file_sb_list_add(f, inode->i_sb);

@@ -745,7 +744,7 @@ cleanup_all:
* here, so just reset the state.
*/
file_reset_write(f);
- mnt_drop_write(mnt);
+ mnt_drop_write(path->mnt);
}
}
file_sb_list_del(f);
@@ -753,8 +752,7 @@ cleanup_all:
f->f_path.mnt = NULL;
cleanup_file:
put_filp(f);
- dput(dentry);
- mntput(mnt);
+ path_put(path);
return ERR_PTR(error);
}

@@ -780,14 +778,14 @@ cleanup_file:
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;
@@ -816,10 +814,17 @@ struct file *nameidata_to_filp(struct nameidata *nd)

/* 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;
}

@@ -830,26 +835,45 @@ struct file *nameidata_to_filp(struct nameidata *nd)
struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags,
const struct cred *cred)
{
- int error;
- struct file *f;
-
- validate_creds(cred);
+ struct path path = { .dentry = dentry, .mnt = mnt };
+ struct file *ret;

/* We must always pass in a valid mount pointer. */
BUG_ON(!mnt);

- error = -ENFILE;
+ 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);
+
+ if (inode->i_op->open)
+ return inode->i_op->open(path->dentry, flags, cred);
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)
{
diff --git a/include/linux/fs.h b/include/linux/fs.h
index dbd860a..fa062a8 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1595,6 +1595,7 @@ 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;
@@ -1989,6 +1990,7 @@ extern long do_sys_open(int dfd, const char __user *filename, int flags,
extern struct file *filp_open(const char *, int, int);
extern struct file *file_open_root(struct dentry *, struct vfsmount *,
const char *, 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);
--
1.7.3.4


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