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From: Chao Li <[email protected]>
To: Michael Paquier <[email protected]>
Cc: Postgres hackers <[email protected]>
Cc: Robert Haas <[email protected]>
Subject: Re: Incorrect errno used in OpenWalSummaryFile()
Date: Mon, 2 Feb 2026 12:07:57 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>



> On Feb 2, 2026, at 11:54, Michael Paquier <[email protected]> wrote:
> 
> Hi all,
> 
> While looking at walsummary.c for a different thread, I have bumped
> into this code:
> OpenWalSummaryFile(WalSummaryFile *ws, bool missing_ok)
> [...]
>    file = PathNameOpenFile(path, O_RDONLY);
>    if (file < 0 && (errno != EEXIST || !missing_ok))
>        ereport(ERROR,
>                (errcode_for_file_access(),
>                 errmsg("could not open file \"%s\": %m", path)));
> 
> And it seems to me that this EEXIST should be an ENOENT?  The top of
> the function also documents that we want to handle an error when a
> summary file does not exist.  The comment makes sense to me, not the
> code.
> 
> It's also worth noting that this function has two callers, both use
> missing_ok = false, meaning that the errno check does not really
> matter today.  If someone plays with this code on HEAD or the
> back-branches and decides to introduce a missing_ok=true call, it
> could matter, so I'd rather not change this function signature.
> 
> This issue has been mentioned here as well, I've just bumped into it
> independently a few hours ago:
> https://www.postgresql.org/message-id/[email protected]
> 
> Regards,
> --
> Michael
> <wal-summary-errno.patch>


I think this is a correct fix.

```
[EEXIST] O_CREAT and O_EXCL are specified and the file exists. 
[ENOENT] O_CREAT is not set and the named file does not exist.
```

Here, the open flag is only O_RDONLY, so we should only expect ENOENT.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/

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