[1/2] busybox: add /dev/std{in, out, err} symlinks to inittab

Message ID 20180404180935.15185-2-joerg.krause@embedded.rocks
State Accepted
Commit 456ea9871ea015fe2c5a7eb79c4762787286fa56
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/busybox/inittab | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Peter Korsgaard May 1, 2018, 7:52 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/busybox/inittab | 4 ++++
 >  1 file changed, 4 insertions(+)

 > diff --git a/package/busybox/inittab b/package/busybox/inittab
 > index 3f49f6bd7a..0f6b8cbe37 100644
 > --- a/package/busybox/inittab
 > +++ b/package/busybox/inittab
 > @@ -19,6 +19,10 @@
 >  ::sysinit:/bin/mkdir -p /dev/pts
 >  ::sysinit:/bin/mkdir -p /dev/shm
 >  ::sysinit:/bin/mount -a
 > +::sysinit:/bin/ln -sf /proc/self/fd /dev/fd
 > +::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin
 > +::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout
 > +::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.
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/busybox/inittab | 4 ++++
 >> 1 file changed, 4 insertions(+)

 >> diff --git a/package/busybox/inittab b/package/busybox/inittab
 >> index 3f49f6bd7a..0f6b8cbe37 100644
 >> --- a/package/busybox/inittab
 >> +++ b/package/busybox/inittab
 >> @@ -19,6 +19,10 @@
 >> ::sysinit:/bin/mkdir -p /dev/pts
 >> ::sysinit:/bin/mkdir -p /dev/shm
 >> ::sysinit:/bin/mount -a
 >> +::sysinit:/bin/ln -sf /proc/self/fd /dev/fd
 >> +::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin
 >> +::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout
 >> +::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.

Committed to 2018.02.x, thanks.

Patch

diff --git a/package/busybox/inittab b/package/busybox/inittab
index 3f49f6bd7a..0f6b8cbe37 100644
--- a/package/busybox/inittab
+++ b/package/busybox/inittab
@@ -19,6 +19,10 @@ 
 ::sysinit:/bin/mkdir -p /dev/pts
 ::sysinit:/bin/mkdir -p /dev/shm
 ::sysinit:/bin/mount -a
+::sysinit:/bin/ln -sf /proc/self/fd /dev/fd
+::sysinit:/bin/ln -sf /proc/self/fd/0 /dev/stdin
+::sysinit:/bin/ln -sf /proc/self/fd/1 /dev/stdout
+::sysinit:/bin/ln -sf /proc/self/fd/2 /dev/stderr
 ::sysinit:/bin/hostname -F /etc/hostname
 # now run any rc scripts
 ::sysinit:/etc/init.d/rcS