[2/2] sysvinit: add /dev/std{in, out, err} symlinks to inittab

Message ID 20180404180935.15185-3-joerg.krause@embedded.rocks
State Accepted
Commit 6919fc55660eafd1a55c2e8535cc9291c251faf5
Headers show
Series
  • Add /dev/std{in, out, err} symlinks to inittabs
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Commit Message

Jörg Krause April 4, 2018, 6:09 p.m.
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/

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
---
 package/sysvinit/inittab | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Comments

Peter Korsgaard May 1, 2018, 7:53 p.m. | #1
>>>>> "Jörg" == Jörg Krause <joerg.krause@embedded.rocks> writes:

 > 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/

 > Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
 > ---
 >  package/sysvinit/inittab | 6 +++++-
 >  1 file changed, 5 insertions(+), 1 deletion(-)

 > diff --git a/package/sysvinit/inittab b/package/sysvinit/inittab
 > index fad91eae8b..608aabce07 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
 > +si6::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin
 > +si7::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout
 > +si8::sysinit:/bin/ln -sf /proc/self/fd/2 /dev/stderr

This will fail on static /dev on a readonly rootfs, so I've redirected
errors to /dev/null.

Committed with that changed, thanks.

I have also added a patch adding these symlinks in the default skeleton
to handle static /dev on readonly rootfs setups.
Peter Korsgaard June 17, 2018, 3:58 p.m. | #2
>>>>> "Peter" == Peter Korsgaard <peter@korsgaard.com> writes:

>>>>> "Jörg" == Jörg Krause <joerg.krause@embedded.rocks> writes:
 >> 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/

 >> Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
 >> ---
 >> package/sysvinit/inittab | 6 +++++-
 >> 1 file changed, 5 insertions(+), 1 deletion(-)

 >> diff --git a/package/sysvinit/inittab b/package/sysvinit/inittab
 >> index fad91eae8b..608aabce07 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
 >> +si6::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin
 >> +si7::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout
 >> +si8::sysinit:/bin/ln -sf /proc/self/fd/2 /dev/stderr

 > This will fail on static /dev on a readonly rootfs, so I've redirected
 > errors to /dev/null.

 > Committed with that changed, thanks.

 > I have also added a patch adding these symlinks in the default skeleton
 > to handle static /dev on readonly rootfs setups.

Committed to 2018.02.x, thanks.

Patch

diff --git a/package/sysvinit/inittab b/package/sysvinit/inittab
index fad91eae8b..608aabce07 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
+si6::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin
+si7::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout
+si8::sysinit:/bin/ln -sf /proc/self/fd/2 /dev/stderr
+si9::sysinit:/bin/hostname -F /etc/hostname
 rcS:12345:wait:/etc/init.d/rcS
 
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