openat2 is a new syscall added to Linux 5.6. It provides a superset of
openat(2) functionality, extending it with flags telling the kernel how
to resolve the paths.
For more info, see https://lwn.net/Articles/803237/
NOTE that this is a second attempt to add the call; the previous one
(https://golang.org/cl/227280) was reverted
(https://golang.org/cl/227846) due to the test case failure on ARM
(https://golang.org/issue/38357).
This CL has the test case reworked to be less assumptive to the testing
environment. In particular, it first tries if the most simplistic
openat2() call succeeds, and skips the test otherwise. It is done that
way because CI can be under under different kernels and in various
envrionments -- in particular, Docker+seccomp can result in EPERM from a
system call (which is not expected otherwise).
For previous discussions about the test case, see
https://golang.org/cl/227865.
Change-Id: I4276cf13dc29ecbdbdc9c58da0f76270f585a67f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/253057
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
openat2 is a new syscall added to Linux 5.6. It provides a superset
of openat(2) functionality, providing a way to extend it in the future,
and (for now) adding flags telling the kernel how to resolve the path.
For more info on openat2, see https://lwn.net/Articles/803237/
A primitive test case is added to check that Openat2 works as
it should. Tested to skip on kernel 5.5 and pass on 5.6.
Change-Id: Ib8bbd71791762f043200543cecdea16d2fd3c81d
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Reviewed-on: https://go-review.googlesource.com/c/sys/+/227280
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Add IoctlRetInt() for ioctls that use syscall's return value
as an output parameter. Add a unit test for Linux, and the
NS_GET_ defines that it requires (see ioctl_ns(2)).
Motivation:
Currently, x/sys/unix provides a few functions to deal with ioctls.
In particular, IoctlGetInt(), which "performs an ioctl operation
which gets an integer value". It does that by passing a pointer
to an integer to a syscall and returning that integer. The value
returned from syscall is treated as success/failure flag
(0 means success, -1 means failure, and in such case errno
is used to figure out the underlying error).
It appears that there are a few ioctls in Linux and at least one
in Solaris, which do not use the above way to return an int, instead
they use the syscall's return value (in case it's not negative).
As Linux ioctl(2) man page says,
> RETURN VALUE
> Usually, on success zero is returned. A few ioctl() requests
> use the return value as an output parameter and return
> a nonnegative value on success. On error, -1 is returned,
> and errno is set appropriately.
Currently I am aware of at least 6 Linux ioctls that do that
(return the value directly):
* LOOP_CTL_* ioctls on /dev/loop-control (all 3 of them). Source: loop(4)
* NS_* ioctls (3 out of 4) on /proc/PID/ns/*. Source: ioctl_ns(2)
And one in Solaris:
* I_FIND ioctl, source: streamio(7i).
There might be some more ioctls like the ones above, but since
ioctls are scarcely documented, it is hard to say how many more.
Obviously, using IoctlGetInt() for such ioctls would be a big
mistake, as 0 will always be returned. For example, there was
a bug in Docker's pkg/loopback (moby/moby#39801).
[v6: make it linux-specific for now]
Fixesgolang/go#33966
Change-Id: Ie64f72fd84101b955ba14519a357e06a66d685d0
Reviewed-on: https://go-review.googlesource.com/c/sys/+/192780
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Kir Kolyshkin