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    Subject[RFC PATCH 02/35] vfs: add path_open()
    Date
    Currently opening an overlay file results in:

    - the real file on the underlying layer being opened
    - f_path being set to the overlay {mount, dentry} pair

    This patch adds a new helper that allows the above to be explicitly
    performed. I.e. it's the same as dentry_open(), except the underlying
    inode to open is given as a separate argument.

    This is in preparation for stacking I/O operations on overlay files.

    Later, when implicit opening is removed, dentry_open() can be implemented
    by just calling path_open().

    Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
    ---
    fs/open.c | 27 +++++++++++++++++++++++++++
    include/linux/fs.h | 2 ++
    2 files changed, 29 insertions(+)

    diff --git a/fs/open.c b/fs/open.c
    index 7ea118471dce..8c315f9ec2f6 100644
    --- a/fs/open.c
    +++ b/fs/open.c
    @@ -866,6 +866,33 @@ int vfs_open(const struct path *path, struct file *file,
    return do_dentry_open(file, d_backing_inode(dentry), NULL, cred);
    }

    +struct file *path_open(const struct path *path, int flags, struct inode *inode,
    + const struct cred *cred)
    +{
    + struct file *file;
    + int retval;
    +
    + file = get_empty_filp();
    + if (!IS_ERR(file)) {
    + file->f_flags = flags;
    + file->f_path = *path;
    + retval = do_dentry_open(file, inode, NULL, cred);
    + if (retval) {
    + put_filp(file);
    + file = ERR_PTR(retval);
    + } else {
    + retval = open_check_o_direct(file);
    + if (retval) {
    + fput(file);
    + file = ERR_PTR(retval);
    + }
    + }
    + }
    +
    + return file;
    +}
    +EXPORT_SYMBOL(path_open);
    +
    struct file *dentry_open(const struct path *path, int flags,
    const struct cred *cred)
    {
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index f0f87f2beb79..c6d7e3b00163 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -2401,6 +2401,8 @@ extern struct file *filp_open(const char *, int, umode_t);
    extern struct file *file_open_root(struct dentry *, struct vfsmount *,
    const char *, int, umode_t);
    extern struct file * dentry_open(const struct path *, int, const struct cred *);
    +extern struct file *path_open(const struct path *, int, struct inode *,
    + const struct cred *);
    extern int filp_close(struct file *, fl_owner_t id);

    extern struct filename *getname_flags(const char __user *, int, int *);
    --
    2.14.3
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