Re: [Xen-devel] [PATCH 22/29] tools/libxl: Allow limiting amount copied by datacopier

[Wen Congyang <wency@xxxxxxxxxxxxxx>]

On 09/11/2014 01:11 AM, Andrew Cooper wrote:
> From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> 
> Add a parameter, maxread, to limit the amount of data read from the
> source fd of a datacopier.
> 
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> ---
>  tools/libxl/libxl_aoutils.c    |    9 +++++++--
>  tools/libxl/libxl_bootloader.c |    2 ++
>  tools/libxl/libxl_dom.c        |    1 +
>  tools/libxl/libxl_internal.h   |    1 +
>  4 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c
> index caba637..6502325 100644
> --- a/tools/libxl/libxl_aoutils.c
> +++ b/tools/libxl/libxl_aoutils.c
> @@ -145,7 +145,7 @@ static void datacopier_check_state(libxl__egc *egc, 
> libxl__datacopier_state *dc)
>                  return;
>              }
>          }
> -    } else if (!libxl__ev_fd_isregistered(&dc->toread)) {
> +    } else if (!libxl__ev_fd_isregistered(&dc->toread) || dc->maxread == 0) {
>          /* we have had eof */
>          datacopier_callback(egc, dc, 0, 0);
>          return;
> @@ -233,7 +233,8 @@ static void datacopier_readable(libxl__egc *egc, 
> libxl__ev_fd *ev,
>          }
>          int r = read(ev->fd,
>                       buf->buf + buf->used,
> -                     sizeof(buf->buf) - buf->used);
> +                     (sizeof(buf->buf) - buf->used) < dc->maxread ?
> +                         (sizeof(buf->buf) - buf->used) : dc->maxread);
>          if (r < 0) {
>              if (errno == EINTR) continue;
>              if (errno == EWOULDBLOCK) break;
> @@ -258,7 +259,11 @@ static void datacopier_readable(libxl__egc *egc, 
> libxl__ev_fd *ev,
>          }
>          buf->used += r;
>          dc->used += r;
> +        dc->maxread -= r;
>          assert(buf->used <= sizeof(buf->buf));
> +        assert(dc->maxread >= 0);
> +        if (dc->maxread == 0)
> +            break;

We can call libxl__ev_fd_deregister() here, and no need to touch 
datacopier_check_state().
Otherwise, datacopier_readable() may be called again, and read() returns 0. And 
then
libxl__ev_fd_deregister() is called.

Thanks
Wen Congyang

>      }
>      datacopier_check_state(egc, dc);
>  }
> diff --git a/tools/libxl/libxl_bootloader.c b/tools/libxl/libxl_bootloader.c
> index 79947d4..1503101 100644
> --- a/tools/libxl/libxl_bootloader.c
> +++ b/tools/libxl/libxl_bootloader.c
> @@ -516,6 +516,7 @@ static void bootloader_gotptys(libxl__egc *egc, 
> libxl__openpty_state *op)
>  
>      bl->keystrokes.ao = ao;
>      bl->keystrokes.maxsz = BOOTLOADER_BUF_OUT;
> +    bl->keystrokes.maxread = INT_MAX;
>      bl->keystrokes.copywhat =
>          GCSPRINTF("bootloader input for domain %"PRIu32, bl->domid);
>      bl->keystrokes.callback =         bootloader_keystrokes_copyfail;
> @@ -527,6 +528,7 @@ static void bootloader_gotptys(libxl__egc *egc, 
> libxl__openpty_state *op)
>  
>      bl->display.ao = ao;
>      bl->display.maxsz = BOOTLOADER_BUF_IN;
> +    bl->display.maxread = INT_MAX;
>      bl->display.copywhat =
>          GCSPRINTF("bootloader output for domain %"PRIu32, bl->domid);
>      bl->display.callback =         bootloader_display_copyfail;
> diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
> index 0dfdb08..2f74341 100644
> --- a/tools/libxl/libxl_dom.c
> +++ b/tools/libxl/libxl_dom.c
> @@ -1717,6 +1717,7 @@ void libxl__domain_save_device_model(libxl__egc *egc,
>      dc->readfd = -1;
>      dc->writefd = fd;
>      dc->maxsz = INT_MAX;
> +    dc->maxread = INT_MAX;
>      dc->copywhat = GCSPRINTF("qemu save file for domain %"PRIu32, 
> dss->domid);
>      dc->writewhat = "save/migration stream";
>      dc->callback = save_device_model_datacopier_done;
> diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> index 03e9978..d93a6ee 100644
> --- a/tools/libxl/libxl_internal.h
> +++ b/tools/libxl/libxl_internal.h
> @@ -2425,6 +2425,7 @@ struct libxl__datacopier_state {
>      libxl__ao *ao;
>      int readfd, writefd;
>      ssize_t maxsz;
> +    ssize_t maxread;
>      const char *copywhat, *readwhat, *writewhat; /* for error msgs */
>      FILE *log; /* gets a copy of everything */
>      libxl__datacopier_callback *callback;
> 


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