Hi,
On Wed, 8 May 2024 at 14:16, Ranier Vilela <ranier.vf@gmail.com> wrote:
>
>
> Em qua., 8 de mai. de 2024 às 04:37, Nazir Bilal Yavuz <byavuz81@gmail.com> escreveu:
>>
>> Hi Ranier,
>>
>> Thanks for looking into this!
>>
>> I am not sure why but your reply does not show up in the thread, so I
>> copied your reply and answered it in the thread for visibility.
>>
>> On Tue, 7 May 2024 at 16:28, Ranier Vilela <ranier.vf@gmail.com> wrote:
>> >
>> > I know it's coming from copy-and-paste, but
>> > I believe the flags could be:
>> > - dstfd = OpenTransientFile(tofile, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
>> > + dstfd = OpenTransientFile(tofile, O_CREAT | O_WRONLY | O_TRUNC | O_EXCL | PG_BINARY);
>> >
>> > The flags:
>> > O_WRONLY | O_TRUNC
>> >
>> > Allow the OS to make some optimizations, if you deem it possible.
>> >
>> > The flag O_RDWR indicates that the file can be read, which is not true in this case.
>> > The destination file will just be written.
>>
>> You may be right about the O_WRONLY flag but I am not sure about the
>> O_TRUNC flag.
>>
>> O_TRUNC from the linux man page [1]: If the file already exists and is
>> a regular file and the access mode allows writing (i.e., is O_RDWR or
>> O_WRONLY) it will be truncated to length 0. If the file is a FIFO or
>> terminal device file, the O_TRUNC flag is ignored. Otherwise, the
>> effect of O_TRUNC is unspecified.
>
> O_TRUNC is usually used in conjunction with O_WRONLY.
> See the example at:
> open.html
>
> O_TRUNC signals the OS to forget the current contents of the file, if it happens to exist.
> In other words, there will be no seeks, only and exclusively writes.
You are right; the O_TRUNC flag truncates the file, if it happens to
exist. But it should not exist in the first place because the code at
[2] should check this before the OpenTransientFile() call. Even if we
assume somehow the check at [2] does not work, I do not think the
correct operation is to truncate the contents of the existing file.
>>
>> But it should be already checked if the destination directory already
>> exists in dbcommands.c file in createdb() function [2], so this should
>> not happen.
>
> I'm not sure what you're referring to here.
Sorry, I meant that the destination directory / file should not exist
because the code at [2] confirms it does not exist, otherwise it
errors out.
--
Regards,
Nazir Bilal Yavuz
Microsoft