[CRIU] Re: [PATCH 3/7] fifo: Add checkpoint restore for fifos v2

[Pavel Emelyanov]

> +static int __open_fifo_fd(struct reg_file_info *rfi)
> +{
> +       struct fifo_info *info = rfi->priv;
> +       int new_fifo, fake_fifo = -1;
> +
> +       /*
> +        * The fifos (except read-write fifos) do wait until
> +        * another pipe-end get connected, so to be able to
> +        * proceed the restoration procedure we open a fake
> +        * fifo here.
> +        */
> +       fake_fifo = open(rfi->path, O_RDWR);
> +       if (fake_fifo < 0) {
> +               pr_perror("Can't open fake fifo %#x [%s]", info->fe.id, rfi->path);
> +               return -1;
> +       }
> +
> +       new_fifo = open(rfi->path, rfi->rfe.flags);
> +       if (new_fifo < 0) {
> +               pr_perror("Can't open fifo %#x [%s]", info->fe.id, rfi->path);
> +               goto out;
> +       }
> +
> +       if (restore_pipe_data(CR_FD_FIFO_DATA, fake_fifo, info->fe.id,
> +                             info->bytes, info->off)) {
> +               close(new_fifo);
> +               new_fifo = -1;
> +       }
> +
> +out:
> +       close(fake_fifo);
> +       return new_fifo;
> +}
> +
> +static int open_fifo_fd(struct file_desc *d)
> +{
> +       struct fifo_info *info = container_of(d, struct fifo_info, d);
> +       struct reg_file_info *rfi;
> +       struct file_desc *rd;
> +
> +       pr_info("\t\tCreating fifo pipe_id=%#x id=%#x\n",
> +               info->fe.pipe_id, info->fe.id);
> +
> +       rd = find_file_desc_raw(FDINFO_REG, info->fe.id);
> +       if (!rd) {
> +               pr_perror("Can't find regfile for fifo %#x\n", info->fe.id);
> +               return -1;
> +       }
> +
> +       rfi = container_of(rd, struct reg_file_info, d);
> +       if (rfi->open != __open_fifo_fd)
> +               rfi->open = __open_fifo_fd;
> +       rfi->priv = info;
> +
> +       return open_fe_fd(rd);

I don't understand the code above. Why do we find another file_desc while
the one we're asked to open is passed to us as an argument?

> +}
> +

> @@ -161,6 +164,22 @@ struct pipe_data_entry {
>         u8      data[0];
>  } __packed;
> 
> +struct fifo_entry {
> +       u32     id;
> +
> +       /*
> +        * FIXME

Why FIXME? ID is an ID of a file, while pipe_id is an ID of fifo inode.
It cannot be fixed at all!

> +        * Since we keep fifo data in the same
> +        * file format as the pipe data, at moment
> +        * all entries are addressed via pipe_id,
> +        * but this should be reworked and both
> +        * pipes data and fifo data should be
> +        * addressed via number through strategy
> +        * and kept in one image on disk.
> +        */
> +       u32     pipe_id;
> +} __packed;
> +
>  /*
>   * splice() connect cache pages to pipe buffer, so
>   * some part of pages may be loosed if data are not
> --
> 1.7.7.6
> 
> .
>