[bug-diffutils] bug#33965: handling of closed file descriptors

[Bruno Haible]

There is a problem with the handling of closed file descriptors
in diff-3.7: As mentioned in [1], the 'new-file' test fails on HP-UX.
An investigation [2] shows that different coding techniques are needed,
depending on the desired outcome for closed file descriptors.

This patch uses a variant of (A) from [2]. Namely, the result of fcntl
can apparently be used to distinguish the substitute file descriptor
stuffed in by exec() from a regular open("/dev/null",O_RDONLY).

[1] https://lists.gnu.org/archive/html/diffutils-devel/2018-12/msg00019.html
[2] https://lists.gnu.org/archive/html/bug-gnulib/2019-01/msg00012.html

0001-Recognize-file-descriptors-closed-by-the-parent-proc.patch
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