[PATCH] examples: disable ucontext-cp if ucontext.h is not available

[PATCH] examples: disable ucontext-cp if ucontext.h is not available

[Simon Zeni]

The header file `ucontext.h` is not available on musl based distros. The
example `ucontext-cp` is not built if `configure` fails to locate the
header.

Signed-off-by: Simon Zeni <simon@bl4ckb0ne.ca>
---

See [this mail][1] from the musl mailing list about why those functions
are not implemented

I also noticed that `make runtests` fails on alpinelinux (5.4.72-0-lts
with musl-1.2.1)

```
Tests failed:  <accept-reuse> <across-fork> <defer> <double-poll-crash>
<file-register> <file-update> <io_uring_enter> <io_uring_register> <lfs-openat>
<lfs-openat-write> <link-timeout> <link_drain> <open-close> <openat2>
<pipe-eof> <poll-cancel> <poll-cancel-ton> <poll-link> <read-write>
<sigfd-deadlock> <sq-poll-dup> <sq-poll-share> <sq-space_left> <timeout>
<statx>
```

I can post a full trace if needed.

Simon

[1]: https://www.openwall.com/lists/musl/2016/02/04/4

 configure         | 21 +++++++++++++++++++++
 examples/Makefile |  6 +++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index c911f59..3b96cde 100755
--- a/configure
+++ b/configure
@@ -287,6 +287,24 @@ if compile_prog_cxx "" "" "C++"; then
 fi
 print_config "C++" "$has_cxx"

+##########################################
+# check for ucontext support
+has_ucontext="no"
+cat > $TMPC << EOF
+#include <ucontext.h>
+int main(int argc, char **argv)
+{
+  ucontext_t ctx;
+  getcontext(&ctx);
+  return 0;
+}
+EOF
+if compile_prog "" "" "has_ucontext"; then
+  has_ucontext="yes"
+fi
+print_config "has_ucontext" "$has_ucontext"
+
+
 #############################################################################

 if test "$__kernel_rwf_t" = "yes"; then
@@ -304,6 +322,9 @@ fi
 if test "$has_cxx" = "yes"; then
   output_sym "CONFIG_HAVE_CXX"
 fi
+if test "$has_ucontext" = "yes"; then
+  output_sym "CONFIG_HAVE_UCONTEXT"
+fi

 echo "CC=$cc" >> $config_host_mak
 print_config "CC" "$cc"
diff --git a/examples/Makefile b/examples/Makefile
index 0eec627..60c1b71 100644
--- a/examples/Makefile
+++ b/examples/Makefile
@@ -10,7 +10,11 @@ ifneq ($(MAKECMDGOALS),clean)
 include ../config-host.mak
 endif

-all_targets += io_uring-test io_uring-cp link-cp ucontext-cp
+all_targets += io_uring-test io_uring-cp link-cp
+
+ifdef CONFIG_HAVE_UCONTEXT
+all_targets += ucontext-cp
+endif

 all: $(all_targets)

--
2.29.1

Re: [PATCH] examples: disable ucontext-cp if ucontext.h is not available

[Jens Axboe]

On 10/27/20 8:31 PM, Simon Zeni wrote:
> The header file `ucontext.h` is not available on musl based distros. The
> example `ucontext-cp` is not built if `configure` fails to locate the
> header.

Thanks, applied.

> I also noticed that `make runtests` fails on alpinelinux (5.4.72-0-lts
> with musl-1.2.1)
> 
> ```
> Tests failed:  <accept-reuse> <across-fork> <defer> <double-poll-crash>
> <file-register> <file-update> <io_uring_enter> <io_uring_register> <lfs-openat>
> <lfs-openat-write> <link-timeout> <link_drain> <open-close> <openat2>
> <pipe-eof> <poll-cancel> <poll-cancel-ton> <poll-link> <read-write>
> <sigfd-deadlock> <sq-poll-dup> <sq-poll-share> <sq-space_left> <timeout>
> <statx>

It's been a while since I double checked 5.4-stable, I bet a lot of these
are due to the tests not being very diligent in checking what is and what
isn't supported. I'll take a look and rectify some of that.

-- 
Jens Axboe

Re: [PATCH] examples: disable ucontext-cp if ucontext.h is not available

[Simon Zeni]

On Wed Oct 28, 2020 at 12:33 PM EDT, Jens Axboe wrote:
> It's been a while since I double checked 5.4-stable, I bet a lot of
> these
> are due to the tests not being very diligent in checking what is and
> what
> isn't supported. I'll take a look and rectify some of that.

I tried with 5.9.1 and fewer tests failed.

```
Tests failed:  <defer> <double-poll-crash> <file-register>
<io_uring_enter> <io_uring_register> <iopoll> <poll-cancel-ton>
<read-write> <rename> <sq-poll-dup> <sq-poll-share> <unlink>
```

It might be due to musl, I'll as I use the library and send the
necessary patches if needed.

Simon

Re: [PATCH] examples: disable ucontext-cp if ucontext.h is not available

[Jens Axboe]

On 10/28/20 6:53 PM, Simon Zeni wrote:
> On Wed Oct 28, 2020 at 12:33 PM EDT, Jens Axboe wrote:
>> It's been a while since I double checked 5.4-stable, I bet a lot of
>> these
>> are due to the tests not being very diligent in checking what is and
>> what
>> isn't supported. I'll take a look and rectify some of that.
> 
> I tried with 5.9.1 and fewer tests failed.
> 
> ```
> Tests failed:  <defer> <double-poll-crash> <file-register>
> <io_uring_enter> <io_uring_register> <iopoll> <poll-cancel-ton>
> <read-write> <rename> <sq-poll-dup> <sq-poll-share> <unlink>
> ```
> 
> It might be due to musl, I'll as I use the library and send the
> necessary patches if needed.

The log for those would be interesting. rename/unlink is probably
me messing up on skipping on not-supported, sq-poll-* ditto. The
others, not sure - if you fail with -1/-12, probably just missing
capability checks.

-- 
Jens Axboe

Re: [PATCH] examples: disable ucontext-cp if ucontext.h is not available

[Simon Zeni]

On Wed Oct 28, 2020 at 3:06 PM EDT, Jens Axboe wrote:
> The log for those would be interesting. rename/unlink is probably
> me messing up on skipping on not-supported, sq-poll-* ditto. The
> others, not sure - if you fail with -1/-12, probably just missing
> capability checks.

There you go
https://paste.sr.ht/~bl4ckb0ne/61a962894091a8442fc7ab66934e22930122ff18

Re: [PATCH] examples: disable ucontext-cp if ucontext.h is not available

[Jens Axboe]

On 10/28/20 7:23 PM, Simon Zeni wrote:
> On Wed Oct 28, 2020 at 3:06 PM EDT, Jens Axboe wrote:
>> The log for those would be interesting. rename/unlink is probably
>> me messing up on skipping on not-supported, sq-poll-* ditto. The
>> others, not sure - if you fail with -1/-12, probably just missing
>> capability checks.
> 
> There you go
> https://paste.sr.ht/~bl4ckb0ne/61a962894091a8442fc7ab66934e22930122ff18

Yeah, so outside of the double-poll-crash which crashes due to some
syzbot mmap magic unrelated to io_uring, all failures are either:

-EPERM: don't properly check for !root
-ENOMEM: user doesn't have a high enough ulimit -l setting
unlink/rename not properly checking kernel level support (fixed this one)

I need to provide a generic queue setup helper that catches the two
general error cases and skips tests (saying why), then it should run
clean there too.

-- 
Jens Axboe