Re: [Qemu-devel] [PATCH v5 2/5] raw-posix: Refactor logical block size detection.

[Stefan Hajnoczi]

On Thu, Dec 18, 2014 at 12:18:01PM +0100, Ekaterina Tumanova wrote:
> +#if defined(BLKSSZGET)
> +#  define SECTOR_SIZE BLKSSZGET
> +#elif defined(DKIOCGETBLOCKSIZE)
> +#  define SECTOR_SIZE DKIOCGETBLOCKSIZE
> +#elif defined(DIOCGSECTORSIZE)
> +#  define SECTOR_SIZE DIOCGSECTORSIZE
> +#else
> +    return -ENOTSUP
> +#endif
> +    if (ioctl(fd, SECTOR_SIZE, sector_size) < 0) {
> +        return -errno;
> +    }
> +    return 0;
> +#undef SECTOR_SIZE

Not a reason to respin, but I would have preferred simply moving the old
code.

I think the new code works because BLKSSZGET is Linux, DKIOCGETBLOCKSIZE
is Mac OS, and DIOCGSECTORSIZE is FreeBSD.

If there is a host OS where more than one ioctl is available and the
first one fails then the new code is broken.  The old code didn't use
#elif so each ioctl had a chance to run.

Also, the name SECTOR_SIZE is misleading.  It's not a sector size value
but the "get sector size" ioctl request code.

Stefan

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