Re: [Qemu-devel] [PATCH v7 11/35] util: introduce qemu_file_getlength()

[Eduardo Habkost]

On Wed, Nov 04, 2015 at 11:17:09AM +0800, Xiao Guangrong wrote:
> 
> 
> On 11/04/2015 07:21 AM, Eduardo Habkost wrote:
> >On Mon, Nov 02, 2015 at 05:13:13PM +0800, Xiao Guangrong wrote:
> >[...]
> >>+size_t qemu_file_getlength(const char *file, Error **errp)
> >>+{
> >>+    int64_t size;
> >[...]
> >>+    return size;
> >
> >Can you guarantee that SIZE_MAX >= INT64_MAX on all platforms supported
> >by QEMU?
> >
> 
> Actually, this function is abstracted from the common function, 
> raw_getlength(),
> in raw-posix.c whose return value is int64_t.
> 
> And i think int64_t is large enough for block devices.

int64_t should be enough, but I don't know if size_t is large enough on
all platforms.

I believe it's going to be either one of those cases:

* If you are absolutely sure SIZE_MAX >= INT64_MAX on all platforms,
  please explain why (and maybe add a QEMU_BUILD_BUG_ON?). (I don't
  think this will be the case)
* If SIZE_MAX < INT64_MAX is possible but you believe
  size <= SIZE_MAX is always true here, please explain why (and maybe
  add an assert()).
* Otherwise, we need to set an appropriate error if size > SIZE_MAX
  or change the type of qemu_file_getlength(). What about making it
  uint64_t?

-- 
Eduardo