Re: [PATCH 0/7] GNU/Linux mount namespace support

Iago López Galeiras
2015-04-20T16:49:46Z

Thanks a lot for the patches!

I've got a small feature request. If the process inside the mount namespace is
running on a chroot I believe it won't work (I couldn't test it because the
patches don't work for me[1]).

The reason I want this feature is that rkt[2] runs several apps in a container,
each one on its own chroot and I'd like to debug programs running there.

Maybe you could detect if it's runinng on a chroot by reading /proc/$PID/root,
comparing it to / and, if they're different, use the former to get the binary.
What do you think about it?

Thanks again.
Cheers.

[1]: Context from an IRC conversation with gbenson: My gdb is multi-threaded and
multi-threaded programs can't change mount namespaces, he is already working on
a fix.

[2]: https://github.com/coreos/rkt

On 04/16/2015 02:19 PM, Gary Benson wrote:
> Hi all,
>
> This series allows GDB and gdbserver on GNU/Linux systems to attach
> to processes in mount namespaces other than the debugger's own when
> invoked with the appropriate permissions. This allows an application
> running in a container to be debugged by running GDB or gdbserver on
> the host, or by running GDB or gdbserver from within another container
> that shares the host's PID namespace.
>
> This series builds on the 'Do not require "file" commands for remote
> targets' series that is currently under review:
>
> https://sourceware.org/ml/gdb-patches/2015-04/msg00015.html
>
> It also requires the 'Do not manipulate "target:" filenames as local
> paths' patch to function correctly:
>
> https://sourceware.org/ml/gdb-patches/2015-04/msg00547.html
>
> A tree with the latest versions of all these patches applied is
> available here:
>
> https://github.com/gbenson/binutils-gdb/tree/namespaces
>
> The patches in this series are as follows:
>
> - Patch 1 (Move make_cleanup_close to common code) is a minor
> refactoring required for patch 3.
>
> - Patch 2 (Introduce target_fileio_set_fs) adds target-layer
> support for systems where different processes can have different
> views of the filesystem. The new function target_fileio_set_fs
> sets the context in which target_filesystem_is_local and the
> other target_fileio_* functions operate, and can be called to
> select the filesystem of a specific inferior or the filesystem
> of the debugger (GDB or gdbserver). The default implementation
> of target_fileio_set_fs does nothing, which means that targets
> where inferiors and the debugger share the same filesystem will
> work without modification.
>
> - Patch 3 (Introduce nat/linux-namespaces.[ch]) introduces some
> shared code that GDB and gdbserver can use to query and enter
> Linux namespaces.
>
> - GDB contained a small amount of namespace-aware code used to
> display a warning. Patch 4 (Remove linux_proc_pid_get_ns)
> replaces the querying part of this code with a call to the
> new code introduced by patch 3.
>
> - Patch 5 (Implement multiple-filesystem support for Linux targets)
> does exactly what it says on the tin. With this patch you can
> attach to processes in containers using the native Linux target
> using, e.g., "gdb -p PID".
>
> - Patch 6 (Implement multiple-filesystem support for remote targets)
> adds remote protocol support for remote targets where different
> processes can have different views of the filesystem. A new
> vFile:setfs packet is introduced that passes the context set using
> target_fileio_set_fs to the remote target. Caching is used to
> avoid sending unnecessary vFile:setfs packets.
>
> - Patch 7 (Implement vFile:setfs in gdbserver) implements the
> vFile:setfs packet in gdbserver. Currently only GNU/Linux systems
> support this; gdbserver on other systems will return empty
> responses in reply to vFile:setfs packets.
>
> Built and regtested on RHEL 6.6 x86_64.
>
> Ok to commit?
>
> Thanks,
> Gary
>
> --
> http://gbenson.net/
>

--

Iago LÃ³pez Galeiras
Software developer @ Endocode AG
iago@endocode.com

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