On Wednesday, December 21, 2011 3:28:42 pm Kostik Belousov wrote:
> On Wed, Dec 21, 2011 at 12:25:18PM -0500, John Baldwin wrote:
> > On Wednesday, December 21, 2011 11:13:10 am Kostik Belousov wrote:
> > > On Wed, Dec 21, 2011 at 10:31:11AM -0500, John Baldwin wrote:
> > > > On Tuesday, December 20, 2011 5:18:58 pm m...@freebsd.org wrote:
> > > > > On Tue, Dec 20, 2011 at 1:49 PM, John Baldwin <j...@freebsd.org>
> > > > > wrote:
> > > > > > Hmm, if these functions are expected to operate like 'write(2)' and
> > > > > > are
> > > > > > supposed to return the number of bytes written, shouldn't their
> > > > > > return value
> > > > > > be 'ssize_t' instead of 'int'? It looks like the system calls
> > > > > > themselves
> > > > > > already do the right thing in setting td_retval[] (they assign a
> > > > > > ssize_t to it
> > > > > > and td_retval[0] can hold a ssize_t on all of our current
> > > > > > platforms). It
> > > > > > would seem that the only change would be to the header and probably
> > > > > > syscalls.master. I guess this would require a symver bump to fix
> > > > > > though.
> > > > >
> > > > > An extended attribute larger than 2GB is a programming abuse, though.
> > > > > Technically int may not be 32 bits but it is on all supported
> > > > > platforms now.
> > > >
> > > > Today it is an abuse. In the 90's a 64-bit off_t was considered an
> > > > abuse by
> > > > some. :)
> > > >
> > > > The type should match the documented behavior. On OS X the set
> > > > operation
> > > > doesn't return a size but instead returns a simple success/failure (0
> > > > or -1)
> > > > for which an int is appropriate. However, the FreeBSD API documents
> > > > that it
> > > > operates like write and consumes the buffer. Note that the size of the
> > > > buffer passed to the 'set' and 'get' operations is a size_t, not an
> > > > int, and
> > > > the 'get' operations already return a ssize_t, not an int.
> > >
> > > Note that read(2)/write(2) do return int. I still have WIP patch to fix
> > > this, but after some conversations with Bruce I am not sure it is worth
> > > finishing.
> >
> > The manpages and /usr/include/unistd.h claim they return ssize_t. Is this
> > related to the changes to make uio_resid a size_t (I thought that went into
> > the tree)? If the problem is that the values read/write return may fall
> > into
> > the range of only an int even on 64-bit platforms, that is different from
> > the
> > return type which is part of the ABI.
> Yes, it is related. The type change for uio was done in advance.
>
> Take a look at the first statement of sys_read() and sys_write():
> if (uap->nbyte > INT_MAX)
> return (EINVAL);
> and at the copyinio(), which is used by scatter/gather versions of i/o
> syscalls to copy in uiovec:
> if (iov->iov_len > INT_MAX - uio->uio_resid) {
> free(uio, M_IOV);
> return (EINVAL);
Fair enough, but that is more of an implementation detail. The API/ABI is still
correct and uses ssize_t. :)
--
John Baldwin
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