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Bill Hawes <whawes@star.net> writes:
|> I'm working on a patch to provide an expandable fd array and have run into an
|> odd problem, apparently in bash. For some reason the shell is using the
|> sys_dupfd2 call to move fd 3 to fd 255, so that it ends up with fds 0, 1, 2, and
|> 255. This of course forces my patch to expand the fd array even though only four
|> descriptors are in use.
|> Can anyone explain why this is being done?
Fd 255 is used internally as a connection to the tty, so that it doesn't
interfere with the use of exec to relocate fds. Bash also allocates high
fds when handling a process substitution `<(foo)', for the same reason.
--
Andreas Schwab "And now for something
schwab@issan.informatik.uni-dortmund.de completely different"
schwab@gnu.org
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On Wed, 25 Mar 1998, Bill Hawes wrote:
> I'm working on a patch to provide an expandable fd array and have run into an
> odd problem, apparently in bash. For some reason the shell is using the
> sys_dupfd2 call to move fd 3 to fd 255, so that it ends up with fds 0, 1, 2, and
> 255. This of course forces my patch to expand the fd array even though only four
> descriptors are in use.
>
> Can anyone explain why this is being done?
When executing a 'script' bash sets its private number of FDs to 255.
It then opens a script file, duplicating the fd to its max FD -1 so
that when it ultimately closes that FD it doesn't close the original
input/output FDs, leaving the shell with no interactive I/O.
Line 692 of shell.c in my version of bash.
Cheers,
Dick Johnson
***** FILE SYSTEM MODIFIED *****
Penguin : Linux version 2.1.90 on an i586 machine (66.15 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.
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