Re: [Qemu-devel] [PATCH for-2.9?] block/file-posix.c: Fix unused variable warning on OpenBSD

[Max Reitz]

On 20.03.2017 19:33, Peter Maydell wrote:
> On OpenBSD none of the ioctls probe_logical_blocksize() tries
> exist, so the variable sector_size is unused. Refactor the
> code to avoid this (and reduce the duplicated code).
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> The alternative would be to move the variable so it was
> local to a code block inside each #ifdef, but this seemed
> a bit nicer anyway.
> 
> Tentatively tagged 'for-2.9' just because this is the only
> warning in the OpenBSD build, but I don't insist on it.

I'm fine with targeting 2.9.

> I've opted to retain the existing behaviour of "try every
> ioctl available and use the last one that works" rather
> than "stop as soon as something worked".
> 
> ---
>  block/file-posix.c | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 53febd3..b980d23 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -219,28 +219,28 @@ static int probe_logical_blocksize(int fd, unsigned int 
> *sector_size_p)
>  {
>      unsigned int sector_size;
>      bool success = false;
> +    int i;
>  
>      errno = ENOTSUP;
> -
> -    /* Try a few ioctls to get the right size */
> +    unsigned long ioctl_list[] = {
>  #ifdef BLKSSZGET
> -    if (ioctl(fd, BLKSSZGET, &sector_size) >= 0) {
> -        *sector_size_p = sector_size;
> -        success = true;
> -    }
> +        BLKSSZGET,
>  #endif
>  #ifdef DKIOCGETBLOCKSIZE
> -    if (ioctl(fd, DKIOCGETBLOCKSIZE, &sector_size) >= 0) {
> -        *sector_size_p = sector_size;
> -        success = true;
> -    }
> +        DKIOCGETBLOCKSIZE,
>  #endif
>  #ifdef DIOCGSECTORSIZE
> -    if (ioctl(fd, DIOCGSECTORSIZE, &sector_size) >= 0) {
> -        *sector_size_p = sector_size;
> -        success = true;
> -    }
> +        DIOCGSECTORSIZE,
>  #endif
> +    };
> +
> +    /* Try a few ioctls to get the right size */
> +    for (i = 0; i < ARRAY_SIZE(ioctl_list); i++) {

On 32-bit, though:

./block/file-posix.c: In function ‘probe_logical_blocksize’:
./qemu/block/file-posix.c:229:19: error: comparison of unsigned
expression < 0 is always false [-Werror=type-limits]

A cast (int)ARRAY_SIZE() would fix that (I had the same problem once...).

Max

> +        if (ioctl(fd, ioctl_list[i], &sector_size) >= 0) {
> +            *sector_size_p = sector_size;
> +            success = true;
> +        }
> +    }
>  
>      return success ? 0 : -errno;
>  }
>

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