Re: pg_preadv() and pg_pwritev()

Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> I want to be able to do synchronous vectored file I/O, so I made
> wrapper macros for preadv() and pwritev() with fallbacks for systems
> that don't have them. Following the precedent of the pg_pread() and
> pg_pwrite() macros, the "pg_" prefix reflects a subtle contract
> change: the fallback paths might have the side effect of changing the
> file position.

In a quick look, seems OK with some nits:

1. port.h cannot assume that <limits.h> has already been included;
nor do I want to fix that by including <limits.h> there. Do we
really need to define a fallback value of IOV_MAX? If so,
maybe the answer is to put the replacement struct iovec and
IOV_MAX in some new header.

2. I'm not really that happy about loading <sys/uio.h> into
every compilation we do, which would be another reason for a
new specialized header that either includes <sys/uio.h> or
provides fallback definitions.

3. The patch as given won't prove anything except that the code
compiles. Is it worth fixing at least one code path to make
use of pg_preadv and pg_pwritev, so we can make sure this code
is tested before there's layers of other new code on top?

regards, tom lane