lkml.org 
[lkml]   [2013]   [Aug]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [RFC PATCH] fs: Add user_file_or_path_at and use it for truncate
    On Tue, Aug 27, 2013 at 4:08 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
    > 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.

    I'm curious what's wrong with the general concept. (I agree that the
    implementation is heinous.)

    If I ever wanted to add a new *at syscall, I'd like to be able to do:

    int sys_whateverat(int dfd, const char __user *name, int flags)
    {
    resolve_the_thing(dfd, name, flags);
    if (it's a file) {
    check fmode;
    } else {
    inode_permission();
    }

    actually_do_something(inode);

    unreference_whatever_i_got();

    return ret;
    }

    thereby killing the fwhatever and whateverat birds with one stone.


    >
    >> + 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.

    ...phew. I wasn't looking forward to testing and debugging my crap :)

    --Andy


    \
     
     \ /
      Last update: 2013-08-28 01:21    [W:3.304 / U:0.032 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site