Re: [Qemu-devel] [Xen-devel] [PATCH RFC 1/3] xen_disk: handle disk files on ramfs/tmpfs

[Ian Campbell]

On Mon, 2012-12-31 at 12:16 +0000, Roger Pau Monne wrote:
> Files that reside on ramfs or tmpfs cannot be opened with O_DIRECT,
> if first call to bdrv_open fails with errno = EINVAL, try a second
> call without BDRV_O_NOCACHE.

Doesn't that risk spuriously turning of NOCACHE on other sorts of
devices as well which (potentially) opens up a data loss issue?

> Signed-off-by: Roger Pau Monné <address@hidden>
> Cc: address@hidden
> Cc: Stefano Stabellini <address@hidden>
> Cc: Anthony PERARD <address@hidden>
> ---
>  hw/xen_disk.c |   16 +++++++++++++---
>  1 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/xen_disk.c b/hw/xen_disk.c
> index e6bb2f2..a159ee5 100644
> --- a/hw/xen_disk.c
> +++ b/hw/xen_disk.c
> @@ -562,7 +562,7 @@ static void blk_alloc(struct XenDevice *xendev)
>  static int blk_init(struct XenDevice *xendev)
>  {
>      struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, 
> xendev);
> -    int index, qflags, info = 0;
> +    int index, qflags, info = 0, rc;
>  
>      /* read xenstore entries */
>      if (blkdev->params == NULL) {
> @@ -625,8 +625,18 @@ static int blk_init(struct XenDevice *xendev)
>          xen_be_printf(&blkdev->xendev, 2, "create new bdrv (xenbus 
> setup)\n");
>          blkdev->bs = bdrv_new(blkdev->dev);
>          if (blkdev->bs) {
> -            if (bdrv_open(blkdev->bs, blkdev->filename, qflags,
> -                        bdrv_find_whitelisted_format(blkdev->fileproto)) != 
> 0) {
> +            rc = bdrv_open(blkdev->bs, blkdev->filename, qflags,
> +                        bdrv_find_whitelisted_format(blkdev->fileproto));
> +            if (rc != 0 && errno == EINVAL) {
> +                /* Files on ramfs or tmpfs cannot be opened with O_DIRECT,
> +                 * remove the BDRV_O_NOCACHE flag, and try to open
> +                 * the file again.
> +                 */
> +                qflags &= ~BDRV_O_NOCACHE;
> +                rc = bdrv_open(blkdev->bs, blkdev->filename, qflags,
> +                        bdrv_find_whitelisted_format(blkdev->fileproto));
> +            }
> +            if (rc != 0) {
>                  bdrv_delete(blkdev->bs);
>                  blkdev->bs = NULL;
>              }