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Message-ID: <20120815172150.GA25062@fieldses.org>
Date: Wed, 15 Aug 2012 13:21:50 -0400
From: "J. Bruce Fields" <bfields@...ldses.org>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, hch@...radead.org,
torvalds@...ux-foundation.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,
goran.cetusic@...il.com, romain@...bokech.com, mszeredi@...e.cz
Subject: Re: [PATCH 01/13] vfs: add i_op->open()
On Wed, Aug 15, 2012 at 05:48:08PM +0200, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@...e.cz>
>
> Add a new inode operation i_op->open(). This is for stacked
Shouldn't that "->open()" be "->dentry_open()" ?
--b.
> 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 | 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
>
> --
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