From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
cc: Sergey Shinderuk <s.shinderuk@postgrespro.ru>,
        pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: pg_preadv() and pg_pwritev()
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Comments: In-reply-to Thomas Munro <thomas.munro@gmail.com>
	message dated "Thu, 14 Jan 2021 08:52:04 +1300"
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Date: Wed, 13 Jan 2021 15:26:45 -0500
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Thomas Munro <thomas.munro@gmail.com> writes:
> On Thu, Jan 14, 2021 at 5:13 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Looks like we need to be more careful about not including pread.c
>> in the build unless it actually has code to contribute.

> I did it that way because it made it easy to test different
> combinations of the replacements on computers that do actually have
> pwrite and pwritev, just by tweaking pg_config.h.  Here's an attempt
> to do it with AC_REPLACE_FUNCS, which avoids creating empty .o files.
> It means that to test the replacements on modern systems you have to
> tweak pg_config.h and also add the relevant .o files to LIBOBJS in
> src/Makefile.global, but that seems OK.

Yeah, this looks better.  Two gripes, one major and one minor:

* You need to remove pread.o and pwrite.o from the hard-wired
part of the list in src/port/Makefile, else they get built
whether needed or not.

* I don't much like this in fd.h:

@@ -46,6 +46,7 @@
 #include <dirent.h>
 
 
+struct iovec;
 typedef int File;

because it makes it look like iovec and File are of similar
status, which they hardly are.  Perhaps more like

 #include <dirent.h>
+ 
+struct iovec;			/* avoid including sys/uio.h here */
 
 
 typedef int File;


I confirm clean builds on Big Sur and Catalina with this.

			regards, tom lane