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Commitc95ede4

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In count_usable_fds(), duplicate stderr not stdin.
We had a complaint that the postmaster fails to start if the invokingprogram closes stdin. That happens because count_usable_fds expectsto be able to dup(0), and if it can't, we conclude there are no freeFDs and go belly-up. So far as I can find, though, there is no otherplace in the server that touches stdin, and it's not unreasonable toexpect that a daemon wouldn't use that file.As a simple improvement, let's dup FD 2 (stderr) instead. Unlike stdin,it *is* reasonable for us to expect that stderr be open; even if we areconfigured not to touch it, common libraries such as libc might try towrite error messages there.Per gripe from Mario Emmenlauer. Given the lack of previous complaints,I'm not excited about pushing this into stable branches, but it seemsOK to squeeze it into v14.Discussion:https://postgr.es/m/48bafc63-c30f-3962-2ded-f2e985d93e86@emmenlauer.de
1 parentce773f2 commitc95ede4

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  • src/backend/storage/file

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‎src/backend/storage/file/fd.c

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -934,7 +934,9 @@ InitTemporaryFileAccess(void)
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* of already_open will give the right answer. In practice, max_to_probe
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* of a couple of dozen should be enough to ensure good results.
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*
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* We assume stdin (FD 0) is available for dup'ing
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* We assume stderr (FD 2) is available for dup'ing. While the calling
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* script could theoretically close that, it would be a really bad idea,
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* since then one risks loss of error messages from, e.g., libc.
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*/
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staticvoid
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count_usable_fds(intmax_to_probe,int*usable_fds,int*already_open)
@@ -978,12 +980,12 @@ count_usable_fds(int max_to_probe, int *usable_fds, int *already_open)
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break;
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#endif
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981-
thisfd=dup(0);
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thisfd=dup(2);
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if (thisfd<0)
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{
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/* Expect EMFILE or ENFILE, else it's fishy */
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if (errno!=EMFILE&&errno!=ENFILE)
986-
elog(WARNING,"dup(0) failed after %d successes: %m",used);
988+
elog(WARNING,"duplicating stderr file descriptor failed after %d successes: %m",used);
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break;
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}
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