Messages in this thread | | | From | Sergiu Iordache <> | Date | Mon, 11 Jul 2011 09:54:42 -0700 | Subject | Re: [PATCH v3 3/3] char drivers: ramoops debugfs entry |
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On Thu, Jul 7, 2011 at 11:43 PM, Marco Stornelli <marco.stornelli@gmail.com> wrote: > 2011/7/8 Greg KH <greg@kroah.com>: >> On Thu, Jul 07, 2011 at 04:27:27PM -0700, Andrew Morton wrote: >>> On Thu, 7 Jul 2011 16:16:43 -0700 >>> Sergiu Iordache <sergiu@google.com> wrote: >>> >>> > Ramoops currently dumps the log of a panic/oops in a memory area which >>> > is known not to be overwritten on restart (for example 1MB starting at >>> > 15MB). The way it works is by dividing the memory area in records of a >>> > set size (fixed at 4K before my patches, configurable after) and by >>> > dumping a record there for each oops/panic. The problem is that right >>> > now you have to access that memory area through other means, such as >>> > /dev/mem, which is not always possible. >>> > >>> > What my patch did was to add a debugfs entry which returns a valid >>> > record each time (a single dump done by ramoops). The first call >>> > returns the first dump. The first call after the last valid dump >>> > returns an empty buffer. . >>> >>> Please fully describe this "record" in the v2 patch changelog. We'll >>> want to review it for endianness, 32/64-bit compat issues, >>> maintainability, extensibility, etc. >>> >>> > After it has returned nothing, the next >>> > calls return records from the start again. >>> >>> That sounds a bit weird. One would expect it to keep returning zero, >>> requiring userspace to lseek or close/open. >>> >>> > The validity of a dump is >>> > checked by looking after the header. Any comments on this approach are >>> > welcome. >>> > >>> > Changing the entry from debugfs to sysfs wouldn't be a problem. If >>> > sysfs is a valid solution I'll come with a patch that updates the >>> > documentation as well along with the sysfs entry. >>> >>> sysfs sounds OK to me. Then again, sysfs is supposed to be >>> one-value-per-file, so using it would be naughty. >>> >>> I dunno, I'd be inclined to abuse the sysfs rule and hope that nobody >>> notices rather than create a fake char device. But there's certainly >>> plenty of precedent for the fake char driver. >> >> No, please don't abuse sysfs that way. >> >> Use debugfs or a char device node. >> >> thanks, >> >> greg k-h >> > > I agree with Greg. I asked to not break the existent way to read data > via /dev/mem because for me it's the right way to do this thing. > However to do an easy *debug* a debugfs entry can be useful. IMHO, a > "production" script/application that use debugfs instead of /dev/mem > in this case is simply broken because the debugfs can't be like a > system call or other kernel interaction mechanism. Debugfs should be > used only for debug. > > Marco
Any consensus/decision on how to go on with this patch idea?
The options that I see right now are: - keep access through /dev/mem only (but access to /dev/mem is sometimes restricted); - keep the debugfs entry as well(as in the patch); - remove the debugfs entry and add a char driver to access the memory using read and seek operations.
+ the rejected(?) options from before
Sergiu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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