Features/DebuginfoFS

DebuginfoFS

Summary

A read-only, internet-mountable filesystem that provides debuginfo (for use with gdb and other debugging tools), and

a client service to mount the debuginfo filesystem when needed.

Owner

• Name: Will Woods
• email: wwoods@redhat.com

Current status

• Targeted release: Fedora 11
• Last updated: January 28, 2009
• Percentage of completion: 30%

Detailed Description

When a program crashes or is otherwise misbehaving, one of the most helpful things to put in a bug report is a traceback of the offending process, gathered by using gdb. GNOME's bug-buddy does this automatically. But without debugging info, the tracebacks are incomplete.

debuginfo-install can be used to install the needed debuginfo packages, but this takes a long time (2-5 minutes) and 95% of the installed data is unused.

This Feature will provide scripts and tools to provide a WebDAV filesystem containing all the debuginfo needed for everything in Fedora, and a service to allow users (or automatic crash-reporting processes - like Features/CrashCatcher) to mount the filesystem when needed.

Benefit to Fedora

By simplifying the process of getting debugging info, we can improve the quality of bug reports, which should make it easier (and faster) to get bugs fixed.

Scope

There will be two main parts to this feature:

1. A debuginfofs-server package, which provides
   • A debuginfofs-server service,
   • Configuration files to specify which distributions (version/arch) to support, and
   • Some documentation on setting up / maintaining the server.
2. A debuginfofs package, which provides
   • A debuginfofs service,
   • Configuration files to specify the location of the server

We should also provide a public debuginfofs server for Fedora users, and pre-configure the service to use that.

How To Test

1. Prepare a debuginfo server

• public instance coming soon

git clone git://fedorapeople.org/~wwoods/debuginfofs.git
cd debuginfofs
vi rsync-fedora-debuginfo.sh # pick an rsync mirror near you
./rsync-fedora-debuginfo.sh # will require 50-100GB in /var!

2. Install / configure debuginfofs on the client

• packages coming soon

git clone git://fedorapeople.org/~wwoods/debuginfofs.git
cd debuginfofs
cp debuginfofs.init /etc/init.d
cp debuginfofs.sysconfig /etc/sysconfig/debuginfofs
vi /etc/sysconfig/debuginfofs # Set DEBUGINFOFS_HOST to the right hostname

3. Mount debuginfofs

sudo service debuginfofs start

4. Crash a program in gdb

[wwoods@metroid debuginfofs]$ gdb $(which sleep)
GNU gdb Fedora (6.8-29.fc10)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i386-redhat-linux-gnu"...
(gdb) set args 999
(gdb) run
Starting program: /bin/sleep 999
[Hit Ctrl-C]
Program received signal SIGINT, Interrupt.
__kernel_vsyscall () at arch/x86/vdso/vdso32/int80.S:16
16	arch/x86/vdso/vdso32/int80.S: No such file or directory.
	in arch/x86/vdso/vdso32/int80.S
Current language:  auto; currently asm
(gdb) bt
#0  __kernel_vsyscall () at arch/x86/vdso/vdso32/int80.S:16
#1  0x008ac430 in __nanosleep_nocancel () from /lib/libc.so.6
#2  0x0804abd3 in xnanosleep (seconds=999) at xnanosleep.c:112
#3  0x080490f6 in main (argc=2, argv=0xbffff514) at sleep.c:150
(gdb)

If everything is working as expected, you will see the function/file names, as above.

User Experience

Getting debuginfo to get a backtrace for a bug report will become much, much easier (and faster), but the process will change slightly.

Dependencies

• We've chosen WebDAV as the network filesystem for this project, so:
  • The server-side requires httpd's Dav module.
  • Client-side requires a FUSE implementation of WebDAV. wdfs is the only one packaged at the moment, but davfs2 could be considered as well.
• A public debuginfofs server will require somewhere around 40GB of disk per Fedora version/arch - a total of 500GB for Fedora (8,9,10) * (i386,x86_64,ppc).
  • Some further work could be done to drastically reduce the amount of disk space needed by only unpacking debuginfo when it is needed - this may be required if the Fedora infrastructure can't spare that much disk space.
  • This would also reduce setup time to near-zero, since we don't have the overhead of unpacking all the RPMs.
• If we need access to the source files as well as the debugging symbols, there will need to be an additional layer on the client-side to find the source files and put them in a place where gdb can find them.

Contingency Plan

None needed - things stay as they are.

Documentation

The gdb info pages and Releases/FeatureBuildId give some background on the Build-Id feature that makes this possible.

Release Notes

There is a new debuginfofs service, which provides debuginfo for all Fedora packages over the Internet.

Comments and Discussion

• See Talk:Features/DebuginfoFS