* Eric Blake wrote on Wed, Jul 21, 2010 at 08:22:15PM CEST: > On 07/21/2010 12:06 PM, Ralf Wildenhues wrote: > >> But maybe we want to do a global: > >> > >> for i in 3 4 5 6 7; do > >> eval exec $i>&- > >> done > > > > (why not just exec 5>&- 6>&- 7>&-?) > > Easier to extend if we wanted to clear out to fd 63 or some such (if seq > were portable, then 'for i in $(seq 63); do...' would be easier than > writing 60 >&- instances). But yeah, it makes more sense to only clear > what we will explicitly use, rather than to clear arbitrarily high.
$ ksh -c '( exec 17>&-)' ksh[1]: exec: 17: not found ksh -c '( fd=17; eval exec $fd\>\&-)' ksh[1]: eval[1]: exec: 17: not found It is not portable to use fds higher than 9, and the above eval had quoting problems too ;-) > > We don't do anything with fds 3 and 4; either we consider them special, > > then shouldn't close them for that historical reason, or we could just > > use them for internal purposes. Or decide now not use them because > > we've never done so (and our users may have come to rely on that fact). > > We also document that users cannot rely on shell 'exec 3>file' to be > preserved over an exec*(2) call (that is, fds 3 or larger may be marked > cloexec when opened by the shell), and that other shells explicitly > close all inherited fds 3 or larger on startup (that is, even if an fd > is not cloexec in the shell's parent, it might be closed rather than > inherited to the shell script body). So, on thinking about it more, > there is no portable way to write a test that relies on external > inheritance of an fd >= 3 opened by the parent of the testsuite; and > within a portable test, you can use only fds 3 or larger only so long as > you stick to shell constructs (you can't expect your C program or a > subsidiary script to see those fds unless you used the shell to > duplicate it onto one of the 3 standard streams). This paragraph assumes that the portability requirements of some user package are roughly the same as those Autoconf assumes for itself, right? > > But anyway this still means that users wanting to pass extra fds to test > > groups, should know that 5, 6, and 7 are reserved by Autotest, at least > > for passing from outside the testsuite. And probably that 5 is better > > avoided inside as well (I'm not sure if that's necessary, but it might > > be at some point). > > Yeah, documenting that fd 5 is reserved for autotest logging may be > worthwhile. But I don't see that holding up 2.67. Of course not. Finishing 2.67 is more important than these details. Cheers, Ralf
