Re: [PATCH] Fix fd leak in pg_dump compression backends when dup()+fdopen() fails

You're correct. All callers invoke pg_fatal() on failure, so the
process exits immediately and the OS reclaims the fd. There is no
live bug worth back-patching on those grounds.

That said, the patch does fix a real diagnostic problem. In the
original code, when dup() fails with EMFILE, the -1 return value is
passed directly to fdopen(), which fails with EBADF. The user sees:

pg_dump: error: could not open output file: Bad file descriptor

which is misleading -- the actual cause is fd exhaustion, not a bad
descriptor. With the patch, errno is preserved correctly, so the
message becomes:

pg_dump: error: could not open output file: Too many open files

which gives the user actionable information.

I'm happy to limit this to HEAD only if back-patching is not
warranted.

Regards,
Jianghua Yang

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> 于2026年3月19日周四 10:08写道：

> Jianghua Yang <yjhjstz(at)gmail(dot)com> writes:
> > == The Bug ==
>
> > All four compression open functions use this pattern when an existing
> > file descriptor is passed in:
>
> > if (fd >= 0)
> > fp = fdopen(dup(fd), mode); /* or gzdopen() */
>
> > if (fp == NULL)
> > return false; /* dup'd fd is leaked here */
>
> > The problem is that dup(fd) and fdopen()/gzdopen() are two separate
> > steps, and their failure modes must be handled independently:
>
> Hmm. You're right that we could leak the dup'd FD, but would it matter?
> I'm pretty sure all these programs will just exit immediately on
> failure.
>
> I'm not averse to improving the code, but I'm not sure there is
> a live bug worth back-patching.
>
> regards, tom lane
>