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    SubjectRe: [PATCH v3 3/3] char drivers: ramoops debugfs entry
    On Thu, Jul 07, 2011 at 04:27:27PM -0700, Andrew Morton wrote:
    > On Thu, 7 Jul 2011 16:16:43 -0700
    > Sergiu Iordache <> 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.


    greg k-h

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