Re: RFC: android logger feedback request
[Posted January 2, 2012 by corbet]
| From: |
| NeilBrown <neilb-AT-suse.de> |
| To: |
| Tim Bird <tim.bird-AT-am.sony.com> |
| Subject: |
| Re: RFC: android logger feedback request |
| Date: |
| Thu, 22 Dec 2011 12:20:26 +1100 |
| Message-ID: |
| <20111222122026.3a0fae36@notabene.brown> |
| Cc: |
| Greg KH <gregkh-AT-suse.de>,
linux-embedded <linux-embedded-AT-vger.kernel.org>,
linux kernel <linux-kernel-AT-vger.kernel.org>,
Arnd Bergmann <arnd-AT-arndb.de>,
john stultz <johnstul-AT-us.ibm.com>,
Brian Swetland <swetland-AT-google.com>,
Kay Sievers <kay.sievers-AT-vrfy.org>,
Lennart Poettering <lennart-AT-poettering.net> |
| Archive‑link: | |
Article |
On Wed, 21 Dec 2011 16:36:21 -0800 Tim Bird <tim.bird@am.sony.com> wrote:
> On 12/21/2011 03:19 PM, Greg KH wrote:
> > That all describes the current code, but you haven't described what's
> > wrong with the existing syslog interface that requires this new driver
> > to be written. And why can't the existing interface be fixed to address
> > these (potential) shortcomings?
>
>
> >> One specific question I have is where is the most appropriate
> >> place for this code to live, in the kernel source tree?
> >> Other embedded systems might want to use this system (it
> >> is simpler than syslog, and superior in some ways), so I don't
> >> think it should remain in an android-specific directory.
> >
> > What way is it superior?
>
> Here are some ways that this code is superior to syslog:
It is certainly nice and simple. It really looks more like a filesystem than
a char device though... though they aren't really files so much as lossy
pipes. I don't think that's a problem though, lots of things in filesystems
don't behave exactly like files.
If you created a 'logbuf' filesystem that used libfs to provide a single
directory in which privileged processes could create files then you wouldn't
need the kernel to "know" the allowed logs: radio, events, main, system.
The size could be set by ftruncate() (by privileged used again) rather than
being hardcoded.
You would defined 'read' and 'write' much like you currently do to create a list of
datagrams in a circular buffer and replace the ioctls by more standard
interfaces:
LOGGER_GET_LOG_BUG_SIZE would use 'stat' and the st_blocks field
LOGGER_GET_LOG_LEN would use 'stat' and the st_size field
LOGGER_GET_NEXT_ENTRY_LEN could use the FIONREAD ioctl
LOGGER_FLUSH_LOG could use ftruncate
The result would be much the same amount of code, but an interface which has
fewer details hard-coded and is generally more versatile and accessible.
NeilBrown
