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From: Haibo Yan <[email protected]>
To: David Steele <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: Pg Hackers <[email protected]>
Subject: Re: Return pg_control from pg_backup_stop().
Date: Tue, 17 Mar 2026 11:50:29 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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Hi David,

Thank you for the clarification. I have now read the code, and overall it looks good to me. I only had one very small comment.

You currently have:
```
memset(controlFile + sizeof(ControlFileData), 0,
       PG_CONTROL_FILE_SIZE - sizeof(ControlFileData));
memcpy(controlFile, ControlFile, sizeof(ControlFileData));
``` 
This is correct, since only the trailing bytes need to be zeroed before the copy.

I was just wondering whether the following might be slightly clearer:
```
memset(controlFile, 0, PG_CONTROL_FILE_SIZE);
memcpy(controlFile, ControlFile, sizeof(ControlFileData));
```

I do not think this is a real issue, though.

Thanks
Haibo

> On Mar 17, 2026, at 12:05 AM, David Steele <[email protected]> wrote:
> 
> On 3/17/26 12:16, Haibo Yan wrote:
> 
>> I have not read the code yet, so this may already be answered there, but I had a question about the proposal itself. This patch protects against a missing backup_label, but what about a wrong one? If a user restores a backup_label file from a different backup, the existence check alone would not detect that. Do we need some consistency check between the returned pg_control copy and the backup_label contents, or is the intended scope here limited to the “missing file” case only?
> 
> Thank you for having a look!
> 
> The goal here is only to check for a missing backup_label. The general problem is that PostgreSQL suggests that removing backup_label might be a good idea so the user does it:
> 
> If you are not restoring from a backup, try removing the file \"%s/backup_label\"
> 
> The user *could* copy a backup_label from another backup and there are ways we could detect that but I feel that should be material for a separate patch.
> 
> Regards,
> -David
> 
> 

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