[Buildroot] [git commit] sysvinit: add /dev/std{in, out, err} symlinks to inittab

[Peter Korsgaard <peter@korsgaard.com>]

commit: https://git.buildroot.net/buildroot/commit/?id=6919fc55660eafd1a55c2e8535cc9291c251faf5
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/master

Some applications, e.g. bashs process subsitution feature, rely on the
convention of `/dev/fd` being a symbolic link to `/proc/self/fd`.

This symbolic link and his companions `/dev/std*` are created by (e)udev [1],
but not by mdev, resulting in the following error when using the following
expression:

```
bash: /dev/fd/62: No such file or directory
```

For the sake of simplicity, lets fix this by creating the symlinks in inittab.
It is only really needed if eudev isn't used, but it doesn't really hurt to
create them even if eudev will recreate them afterwards.

Note, that we do not create the symlink `/dev/core` as `/proc/kcore` is
not available on all platforms, e.g. ARM, and the feature is not much
appreciated [2].

[1] https://github.com/gentoo/eudev/blob/8943501993322c59a6eb5be456b0d716aafff21e/src/shared/dev-setup.c#L35-L40
[2] https://lwn.net/Articles/45315/

[Peter: redirect errors to /dev/null for ro rootfs]
Signed-off-by: J??rg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
---
 package/sysvinit/inittab | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/package/sysvinit/inittab b/package/sysvinit/inittab
index fad91eae8b..7eaef59d9e 100644
--- a/package/sysvinit/inittab
+++ b/package/sysvinit/inittab
@@ -9,7 +9,11 @@ si1::sysinit:/bin/mount -o remount,rw /
 si2::sysinit:/bin/mkdir -p /dev/pts
 si3::sysinit:/bin/mkdir -p /dev/shm
 si4::sysinit:/bin/mount -a
-si5::sysinit:/bin/hostname -F /etc/hostname
+si5::sysinit:/bin/ln -sf /proc/self/fd /dev/fd 2>/dev/null
+si6::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin 2>/dev/null
+si7::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout 2>/dev/null
+si8::sysinit:/bin/ln -sf /proc/self/fd/2 /dev/stderr 2>/dev/null
+si9::sysinit:/bin/hostname -F /etc/hostname
 rcS:12345:wait:/etc/init.d/rcS
 
 # S0:1:respawn:/sbin/getty -L ttyS0 115200 vt100 # GENERIC_SERIAL