[Libguestfs] [libnbd PATCH 01/20] fuse: Only support defined fallocate modes

[Eric Blake]

On Tue, Jun 08, 2021 at 09:53:42AM +0200, Martin Kletzander wrote:
> None of them is defined on FreeBSD, for example, and the only other way to make
> the code compile would be to define it ourselves.
> 
> Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
> ---
>  fuse/operations.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fuse/operations.c b/fuse/operations.c
> index de04ba7b6d72..098613f66f33 100644
> --- a/fuse/operations.c
> +++ b/fuse/operations.c
> @@ -440,6 +440,9 @@ nbdfuse_fallocate (const char *path, int mode, off_t offset, off_t len,
>    if (readonly)
>      return -EACCES;
>  
> +#if defined(FALLOC_FL_PUNCH_HOLE) || defined(FALLOC_FL_ZERO_RANGE)
> +# if defined(FALLOC_FL_PUNCH_HOLE)

I like this indentation of preprocessor directives...

> +
>    if (mode & FALLOC_FL_PUNCH_HOLE) {
>      if (!nbd_can_trim (nbd.ptr[0]))
>        return -EOPNOTSUPP;       /* Trim not supported. */
> @@ -448,6 +451,9 @@ nbdfuse_fallocate (const char *path, int mode, off_t offset, off_t len,
>        return 0;
>      }
>    }
> +#endif /*# if defined(FALLOC_FL_PUNCH_HOLE) */
> +
> +#if defined(FALLOC_FL_ZERO_RANGE)

...but you forgot it here

>    /* As of FUSE 35 this is not supported by the kernel module and it
>     * always returns EOPNOTSUPP.
>     */
> @@ -470,7 +476,9 @@ nbdfuse_fallocate (const char *path, int mode, off_t offset, off_t len,
>        return 0;
>      }
>    }
> +#endif /* defined(FALLOC_FL_ZERO_RANGE) */

...as well as here.

>    else
> +#endif /* defined(FALLOC_FL_PUNCH_HOLE) || defined(FALLOC_FL_ZERO_RANGE) */
>      return -EOPNOTSUPP;
>  }

To some extent, it would also be possible to write:

#ifndef FALLOC_FL_PUNCH_HOLE
# define FALLOC_FL_PUNCH_HOLE 0
#endif
#ifndef FALLOC_FL_ZERO_RANGE
# define FALLOC_FL_ZERO_RANGE 0
#endif

static int
nbdfuse_fallocate(...) { ...

  if (mode & FALLOC_FL_PUNCH_HOLE) {
    ...
  }
  else if (mode & FALLOC_FL_ZERO_RANGE) {
    ...
  }
  else
    return -EOPNOTSUPP;
}

for fewer in-function #ifdefs, but that is a style choice, not a
correctness issue, so I won't insist.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org