From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Allowing printf("%m") only where it actually works
Date: Sat, 18 Aug 2018 16:34:50 -0400
Message-ID: <13183.1534624490@sss.pgh.pa.us> (raw)
In-Reply-To: <1437.1534100930@sss.pgh.pa.us>
References: <20180528150125.j2x3mp62ssbeg3h5@alvherre.pgsql>
<2685.1527520461@sss.pgh.pa.us>
<8770.1533931511@sss.pgh.pa.us>
<16896.1533935042@sss.pgh.pa.us>
<14925.1534040609@sss.pgh.pa.us>
<1437.1534100930@sss.pgh.pa.us>
I wrote:
> Consider the following approach:
> 1. Teach src/port/snprintf.c about %m. While I've not written a patch
> for this, it looks pretty trivial.
> 2. Teach configure to test for %m and if it's not there, use the
> replacement snprintf. (Note: we're already forcing snprintf replacement
> in cross-compiles, so the added run-time test isn't losing anything.)
> 3. Get rid of elog.c's hand-made substitution of %m strings, and instead
> just let it pass the correct errno value down. (We'd likely need to do
> some fooling in appendStringInfoVA and related functions to preserve
> call-time errno, but that's not complicated, nor expensive.)
> 4. (Optional) Get rid of strerror(errno) calls in favor of %m, even in
> frontend code.
So I started to hack on this, and soon noticed that actually, what elog.c
replaces %m with is *not* the result of strerror(), it's the result of
useful_strerror(). Which, primarily, does this:
/*
* Some strerror()s return an empty string for out-of-range errno. This
* is ANSI C spec compliant, but not exactly useful. Also, we may get
* back strings of question marks if libc cannot transcode the message to
* the codeset specified by LC_CTYPE. If we get nothing useful, first try
* get_errno_symbol(), and if that fails, print the numeric errno.
*/
I don't know offhand whether glibc's implementation delivers anything
useful for out-of-range errno, but I do know that we've seen the
transcoding problem with it, cf commit 8e68816cc which arose from
this discussion:
https://www.postgresql.org/message-id/flat/2782A2665E8342DF8695F396DBA80C88%40maumau
We could easily move useful_strerror() into snprintf.c, I think
(might need to move pgwin32_socket_strerror there too). But then
we'd lose its functionality when using glibc.
So now I'm about ready to propose that we just *always* use
snprintf.c, and forget all of the related configure probing.
This'd have some advantages, notably that we'd get the
useful_strerror() behavior in frontend as well as backend,
assuming we converted all our frontend code to use %m.
And we'd not exactly be the first project to decide that.
But it's kind of a big move from where we are today.
Thoughts?
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, thomas.munro@enterprisedb.com, alvherre@2ndquadrant.com, pgsql-hackers@lists.postgresql.org
Subject: Re: Allowing printf("%m") only where it actually works
In-Reply-To: <13183.1534624490@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox