Something utterly bizarre is going on - if I add a line warn "flags '$flags'"; in lockf() just above the return statement, it works, even with the eval!

It happens on different machines, all debian stable 64bit . I will try a vanilla perl tomorrow. From strace, the length parameter which I'm trying to pass through pack as 0 is (sometimes) corrupted. strace when it goes wrong:

root@geedorah:~# strace perl foo.pl  2>&1 |grep fcntl
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fcntl(3, F_SETLK, {type=F_WRLCK, whence=SEEK_SET, start=0, len=-858311
+8848}) = -1 EINVAL (Invalid argument)
fcntl(3, F_SETLK, {type=F_UNLCK, whence=SEEK_SET, start=0, len=0}) = 0
root@geedorah:~#
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And when it goes right:

root@geedorah:~# strace perl foo.pl  2>&1 |grep fcntl
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fcntl(3, F_SETLK, {type=F_WRLCK, whence=SEEK_SET, start=0, len=0}) = 0
fcntl(3, F_SETLK, {type=F_UNLCK, whence=SEEK_SET, start=0, len=0}) = 0
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