Feedback-ID: ia2694551:Fastmail
Date: Wed, 29 Nov 2023 18:29:15 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: laurenz.albe@cybertec.at, sri@ebi.ac.uk,
	pgsql-general@lists.postgresql.org
Subject: Re: Could not read from file "pg_subtrans/00F5" at offset 122880:
 Success.
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On 2023-Nov-28, Kyotaro Horiguchi wrote:

> By the way, just out of curiosity, but errno should not be zero at the
> time the message above was output, yet "%m" is showing "success",
> which implies errno = 0 in Linux. How can that happen?

If the file is exactly of the length given then seek will work, and read
will not set errno but return a length of 0 bytes.  So
SlruPhysicalReadPage sets SLRU_READ_FAILED and then in pg11 the %m in
SlruReportIOError expands to "Success".

The code in master is completely different (it uses pg_pread rather than
seek + read): it does test for errno and reports accordingly.

So, nothing to do here.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/