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    SubjectRe: [PATCH 6/7 v3] overlay: hybrid overlay filesystem prototype
    On Fri, Sep 24, 2010 at 04:33:05PM +0200, Jens Axboe wrote:
    > On 2010-09-23 01:21, Valerie Aurora wrote:
    > > On Mon, Sep 20, 2010 at 08:04:10PM +0200, Miklos Szeredi wrote:
    > >> From: Miklos Szeredi <mszeredi@suse.cz>
    > >>
    > >> This overlay filesystem is a hybrid of entirely filesystem based
    > >> (unionfs, aufs) and entierly VFS based (union mounts) solutions.
    > >
    > > [...]
    > >
    > >> +static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
    > >> +{
    > >> + struct file *old_file;
    > >> + struct file *new_file;
    > >> + int error = 0;
    > >> +
    > >> + if (len == 0)
    > >> + return 0;
    > >> +
    > >> + old_file = path_open(old, O_RDONLY);
    > >> + if (IS_ERR(old_file))
    > >> + return PTR_ERR(old_file);
    > >> +
    > >> + new_file = path_open(new, O_WRONLY);
    > >> + if (IS_ERR(new_file)) {
    > >> + error = PTR_ERR(new_file);
    > >> + goto out_fput;
    > >> + }
    > >> +
    > >> + /* FIXME: copy up sparse files efficiently */
    > >> + while (len) {
    > >> + loff_t offset = new_file->f_pos;
    > >> + size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
    > >> + long bytes;
    > >> +
    > >> + if (len < this_len)
    > >> + this_len = len;
    > >> +
    > >> + if (signal_pending_state(TASK_KILLABLE, current))
    > >> + return -EINTR;
    > >> +
    > >> + bytes = do_splice_direct(old_file, &offset, new_file, this_len,
    > >> + SPLICE_F_MOVE);
    > >
    > > Interruptible copyup is good. But it looks like splice setup is kind
    > > of heavyweight and we should do it as seldom as possible.
    > >
    > > What about implementing splice flag SPLICE_F_INTERRUPTIBLE instead?
    >
    > The pipe alloc and such? That is lazily done and sticks around.

    Thanks! So this looks like a good way to implement interruptible
    in-kernel file copyup?

    -VAL


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