Re: sendfile -EOVERFLOW on AMD64

[Jakub Jelinek <jakub@redhat.com>]

On Wed, May 19, 2004 at 02:44:27PM +0200, Andi Kleen wrote:
> > (note error is int, not ssize_t), but I don't see anything obvious
> > for other filesystems.
> 
> sendfile64 on 32bit hosts seems to be quite fishy too.
> 
> It works with ssize_t, which is 32bit only, but there are no checks
> that the transfered file is not >4GB.  It would just wrap in this case.
> It would be better to add such checks for 32bit hosts to sendfile64.
> 
> Or am I missing something?

The userland prototypes are:
extern ssize_t sendfile (int __out_fd, int __in_fd, off_t *__offset,
                         size_t __count) __THROW;
extern ssize_t sendfile64 (int __out_fd, int __in_fd, __off64_t *__offset,
                           size_t __count) __THROW;
Thus you really cannot transfer more than 4G-1 bytes in one call on 32-bit
arches.
Actually, already any counts >= 2GB-1 might be problematic, but we are
there on the same boat as with e.g. read(2).  For read, POSIX says:
"If the value of nbyte is greater than {SSIZE_MAX}, the result is
implementation-defined."
so portable programs really shouldn't try to transfer more than that
in one go but the kernel certainly should try to handle sizes up to
SIZE_MAX-4096 or something like that.

	Jakub