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    SubjectRe: [RFC PATCH] fs: Add user_file_or_path_at and use it for truncate
    On Tue, Aug 27, 2013 at 12:16:34PM -0700, Andy Lutomirski wrote:
    > This is an experiment to see if we can get nice semantics for all syscalls
    > that either follow symlinks or allow AT_EMPTY_PATH without jumping through
    > enormous hoops. This converts truncate (although you can't tell using
    > truncate from coreutils, because it actually uses open + ftruncate).
    >
    > The basic idea is that there's a new helper function
    > user_file_or_path_at. It takes an fd and a path and, depending on
    > flags, the emptiness of the path, and whether path is a magic /proc
    > symlink (or a symlink to a magic /proc/symlink), it returns either a
    > struct path or a struct file *.

    No.

    > + path_get(&nd->path);
    > + if (nd->flags & LOOKUP_FILE) {
    > + if (nd->last_symlink_file)
    > + fput(nd->last_symlink_file);
    > + nd->last_symlink_file = file;

    This is ugly (and costs quite a bit of overhead)

    > -static int proc_cwd_link(struct dentry *dentry, struct path *path)
    > +static int proc_cwd_link(struct dentry *dentry, struct file_or_path *link)

    ... and this is even more vile. Vetoed, for being too ugly to live.

    I think I've a saner approach, not involving anything that ugly; I'll post
    a writeup later tonight.


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