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    SubjectRe: [PATCH 6/7 v3] overlay: hybrid overlay filesystem prototype
    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.

    --
    Jens Axboe



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