Re: [PATCH] Name shared memory segments in a more portable way

On 10/25/2011 01:50 AM, Kinkie wrote:
> On Tue, Oct 25, 2011 at 8:05 AM, Kinkie <gkinkie_at_gmail.com> wrote:
>> On Tue, Oct 25, 2011 at 7:33 AM, Alex Rousskov
>> <rousskov_at_measurement-factory.com> wrote:
>>> Hello,
>>>
>>> This patch should make shm_open() work on FreeBSD and some other
>>> OSes. It is untested beyond test-builds.sh on Linux, but is based on
>>> working boost::interprocess code. The preamble has the details.
>>>
>>
>> I'm giving it a spin in the build farm on freebsd and openbsd.

Thank you.

> It's building but failing unit tests:
> FreeBSD:
> http://build.squid-cache.org/job/3.ALPHA-PATCH-amd64-FreeBSD-7.2/20/consoleText

There are two problems here:

1) I guessed the return value of shm_portable_segment_name_is_path wrong
for FreeBSD v7+ jails (at least).

2) Fixing #1 exposes a more serious problem:

> Fatal: Ipc::Mem::Segment::create failed to shm_open(/usr/local/squid/var/run/squidtestRock__testRockSearch): (2) No such file or directory

Here, our "use PREFIX for FreeBSD segment names" logic kicks in as it
should, but the test fails because there is no /usr/local/squid/var/run/
when/where the test runs. PREFIX-based names do not work for tests. I
see two possible solutions:

A) Create a special "we are in a test mode", "use current dir", or a
similar flag so that shm_open can use current dir for shared segments
during testing. Special flags are ugly, but this will allow general code
to continue to use path-agnostic names for shared segments.

B) Switch to path-based names for shared segments in the general code.
When general code needs to name a segment, it will call a
Segment::GenerateName()-like functions explicitly. The shm_open() code
itself will no longer try to add a path when needed. This will make the
general code a little more complex, but the test cases can then use
names that do not start with a slash. This is what Store test cases
already do for cache_dir names.

I favor (B) because it is cleaner and more flexible, even though it is
more work.

Any better ideas?

> OpenBSD:
> http://build.squid-cache.org/view/c-experimental/job/3.ALPHA-PATCH-i386-OpenBSD/7/consoleText

"Duplicate fake segment creation" is a different bug that this patch is
not trying to fix.

Thank you,

Alex.
Received on Tue Oct 25 2011 - 15:13:01 MDT