On Wed, 13 Mar 2013 15:16:25 +0100 Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> Add a new inode operation i_op->dentry_open(). This is for stacked filesystems
> that want to return a struct file from a different filesystem.
>
> ...
>
> +/**
> + * 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);
> + }
> +}
This looks like it will add some overhead to dentry_open(). That long
walk path->dentry->d_inode->i_op->dentry_open, particularly. Can we do
anything? Using filp->f_inode might save a tad.
It's unfortunate and a bit ugly that ->dentry_open() and
do_dentry_open() don't have the same arguments. One would expect and
like them to do so, and this difference raises suspicions about design
warts.
If they _did_ have the same signature then we could perhaps populate
->dentry_open with do_dentry_open by default and avoid the `if'.
The test of inode->i_op->dentry_open could do with an unlikely(), but
that won't save us :(
> +EXPORT_SYMBOL(vfs_open);
Did you consider EXPORT_SYMBOL_GPL()?
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