From: Gabriel Goller <g.goller@proxmox.com>
To: Christian Ebner <c.ebner@proxmox.com>
Cc: pbs-devel@lists.proxmox.com
Subject: Re: [pbs-devel] [PATCH proxmox-backup v2] client: mount: flush output before exiting
Date: Tue, 18 Jun 2024 14:29:16 +0200 [thread overview]
Message-ID: <20240618122916.l4cvteseewltnjht@luna.proxmox.com> (raw)
In-Reply-To: <01d2ebe6-706e-4b8f-8b4a-d351423b9874@proxmox.com>
On 18.06.2024 13:41, Christian Ebner wrote:
>On 6/18/24 13:20, Friedrich Weber wrote:
>>Thanks for tackling this! I ran into this issue (sometimes missing error
>>output) when I was running `sudo proxmox-backup-client mount [...]` and
>>forgot that PBS_REPOSITORY was not passed through by sudo. It looks like
>>in this case, the patch doesn't completely fix this issue -- seems like
>>I'm still missing the error output sometimes:
>>
>>$ sudo ./proxmox-backup-client mount \
>> "$SNAPSHOT" $FILE $PATH \
>> --keyfile $KEYFILE --ns $NS
>>$ sudo ./proxmox-backup-client mount \
>> "$SNAPSHOT" $FILE $PATH \
>> --keyfile $KEYFILE --ns $NS
>>$ sudo ./proxmox-backup-client mount \
>> "$SNAPSHOT" $FILE $PATH \
>> --keyfile $KEYFILE --ns $NS
>>Error: unable to get (default) repository
>
>Hi Friedrich,
>I just double checked by invoking the command in a for loop 10 times,
>for all of which I do get the error message as output.
>
>```bash
>for i in $(seq 0 9)
>do
> sudo proxmox-backup-client mount ct/100/2024-06-13T10:38:54Z root.pxar /mnt
>done
>```
>
>Interestingly, I do also get the output without the patch applied, so
>therefore I did not notice (and obviously forgot to do the negative
>test during review).
>
>Maybe some difference in setup?
>
>Cheers,
>Chris
Hmm I think I know what happens...
This patch is flaky for me as well, sometimes it works, sometimes it
doesn't. The problem is that we move the `pw` file descriptor to
`mount_do`, which means that after it returns, the file_descriptor gets
dropped.
let (pr, pw) = proxmox_sys::pipe()?;
let pr: OwnedFd = pr.into(); // until next sys bump
let pw: OwnedFd = pw.into();
match unsafe { fork() } {
Ok(ForkResult::Parent { .. }) => {
drop(pw);
// Blocks the parent process until we are ready to go in the child
let _res = nix::unistd::read(pr.as_raw_fd(), &mut [0]).unwrap();
Ok(Value::Null)
}
Ok(ForkResult::Child) => {
drop(pr);
nix::unistd::setsid().unwrap();
let result = proxmox_async::runtime::main(mount_do(param, Some(pw)));
^^^
pw gets dropped here, which means the fd is closed.
io::stdout().flush()?;
io::stderr().flush()?;
result
}
Err(_) => bail!("failed to daemonize process"),
}
In the parent process we read from the fd—which is then closed—meaning
that the parent exits at the same time as we do the stderr/stdout flush.
And actually this patch was stupid to begin with, because we don't even
print the error in the mound_do function, but later in the api-handler
:(.
I think we need to do something like this:
if let Err(e) = nix::unistd::read(pr.as_raw_fd(), &mut [0]) {
// if the fd is closed, or some other error happens, wait so
// that the child can return the error safely, then exit
nix::sys::wait::wait().unwrap();
}
Ok(Value::Null)
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next prev parent reply other threads:[~2024-06-18 12:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-14 9:39 Gabriel Goller
2024-06-14 9:54 ` Christian Ebner
2024-06-18 11:20 ` Friedrich Weber
2024-06-18 11:41 ` Christian Ebner
2024-06-18 12:29 ` Gabriel Goller [this message]
2024-06-18 13:00 ` Christian Ebner
2024-06-18 13:10 ` Gabriel Goller
2024-06-18 12:32 ` Friedrich Weber
2024-06-18 12:42 ` Christian Ebner
2024-06-18 12:53 ` Gabriel Goller
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