Re: [Qemu-devel] [PATCH for-2.10 07/16] block/file-posix: Generalize raw_regular_truncate

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Mon, Mar 13, 2017 at 10:40:36PM +0100, Max Reitz wrote:
> Currently, raw_regular_truncate() is intended for setting the size of a
> newly created file. However, we also want to use it for truncating an
> existing file in which case only the newly added space (when growing)
> should be preallocated.
> 
> This also means that if resizing failed, we should try to restore the
> original file size. This is important when using preallocation.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block/file-posix.c | 73 ++++++++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 60 insertions(+), 13 deletions(-)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 35a9e43f3e..cd229324ba 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1384,11 +1384,39 @@ static void raw_close(BlockDriverState *bs)
>      }
>  }
>  
> -static int raw_regular_truncate(int fd, int64_t offset, PreallocMode prealloc,
> +/**
> + * Truncates the given regular file @fd to @offset and, when growing, fills the
> + * new space according to @prealloc.
> + *
> + * @create must be true iff the file is new. In that case, @bs is ignored. If
> + * @create is false, @bs must be valid and correspond to the same file as @fd.

Returns: 0 on success, -errno on failure.

> + */
> +static int raw_regular_truncate(int fd, BlockDriverState *bs, int64_t offset,

The presence of both a file descriptor and a BlockDriverState (actually
it must be a BDRVRawState) arguments is unusual.  It seems bs is needed
for bdrv_getlength().

How about using fstat(fd, &st) and then dropping bs and create?

> +                                PreallocMode prealloc, bool create,
>                                  Error **errp)
>  {
>      int result = 0;
> -    char *buf;
> +    int64_t current_length = 0;
> +    char *buf = NULL;
> +
> +    assert(create || bs);
> +    if (!create) {
> +        BDRVRawState *s = bs->opaque;
> +        assert(s->fd == fd);
> +    }
> +
> +    if (!create) {
> +        current_length = bdrv_getlength(bs);
> +        if (current_length < 0) {
> +            error_setg_errno(errp, -current_length,
> +                             "Could not inquire current length");
> +            return -current_length;
> +        }
> +
> +        if (current_length > offset && prealloc != PREALLOC_MODE_OFF) {
> +            return -ENOTSUP;
> +        }

Missing error_setg().

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