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Andrew Tridgell
ce0f6d5a25
The HAVE_PROC_SELF_FD probe checked that readlink of a DIRECTORY's entry
returned the right path, which is not evidence of an inode pin, and two
platforms fail that assumption in opposite directions:
* NetBSD makes the entry a symlink for directories only -- readlink of
a regular file's entry fails with EINVAL -- so the probe passed and
then every pull of a file died in the post-pin check with
"post-pin readlink failed (race?): f1 Invalid argument". This is
not new: the same failure reproduces on the branch base.
* Cygwin's readlink returns the right path, but opening the magic link
RE-RESOLVES it. Renaming a directory out from under a held fd lets
the magic link reach the replacement, so the pin protected nothing
while appearing to. rrsync-sender-leaf-flip caught this as a real
outside-content leak, not as flakiness.
Only Linux provides the inode-bound magic link this depends on, so
require that explicitly and keep the runtime probes as a guard for
Linux-like environments where /proc is absent or restricted. Elsewhere
rrsync falls through to the unpinned path, as it already did on the BSDs
and macOS. proc_self_fd_pins() mirrors the rule so the race tests skip
rather than report the intended gap, and Cygwin's workflow expects both
of them to skip -- rrsync-symlink only ran there because the old probe
wrongly reported support.