Re: [Qemu-devel] [RFC PATCH 14/17] block: support FALLOC_FL_PUNCH_HOLE trimming

[Stefan Hajnoczi]

On Thu, Mar 8, 2012 at 5:15 PM, Paolo Bonzini <address@hidden> wrote:
> This will enable discard on more filesystems, including ext4.
>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  block/raw-posix.c |   29 ++++++++++++++++++++++++-----
>  1 files changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 2d1bc13..f23d92b 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -52,6 +52,7 @@
>  #include <sys/param.h>
>  #include <linux/cdrom.h>
>  #include <linux/fd.h>
> +#include <linux/falloc.h>
>  #endif
>  #if defined (__FreeBSD__) || defined(__FreeBSD_kernel__)
>  #include <sys/disk.h>
> @@ -131,6 +132,7 @@ typedef struct BDRVRawState {
>  #endif
>     uint8_t *aligned_buf;
>     unsigned aligned_buf_size;
> +    bool has_discard : 1;
>  #ifdef CONFIG_XFS
>     bool is_xfs : 1;
>  #endif
> @@ -257,11 +259,9 @@ static int raw_open_common(BlockDriverState *bs, const 
> char *filename,
>     }
>
>  #ifdef CONFIG_XFS
> -    if (platform_test_xfs_fd(s->fd)) {
> -        s->is_xfs = 1;
> -    }
> +    s->is_xfs = platform_test_xfs_fd(s->fd);
>  #endif
> -
> +    s->has_discard = 1;
>     return 0;
>
>  out_free_buf:
> @@ -605,15 +605,34 @@ static int xfs_discard(BDRVRawState *s, int64_t 
> sector_num, int nb_sectors)
>  static coroutine_fn int raw_co_discard(BlockDriverState *bs,
>     int64_t sector_num, int nb_sectors)
>  {
> -#ifdef CONFIG_XFS
>     BDRVRawState *s = bs->opaque;
> +    int retval;
>
> +    if (s->has_discard == 0) {
> +        return -ENOTSUP;
> +    }
> +#ifdef CONFIG_XFS
>     if (s->is_xfs) {
>         return xfs_discard(s, sector_num, nb_sectors);
>     }
>  #endif
>
> +#ifdef FALLOC_FL_PUNCH_HOLE
> +    retval = fallocate(s->fd, FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE,
> +                       sector_num << 9, (int64_t)nb_sectors << 9);

I'm concerned about introducing blocking syscalls in coroutine code
paths.  This needs to be done asynchronously.

Stefan