Re: [PATCH 2/3] mwifiex: support sysfs initiated device coredump

[Arend van Spriel]

On 2/21/2018 11:59 PM, Brian Norris wrote:
> On Wed, Feb 21, 2018 at 11:50:19AM +0100, Arend van Spriel wrote:
> > Since commit 3c47d19ff4dc ("drivers: base: add coredump driver ops")
> > it is possible to initiate a device coredump from user-space. This
> > patch adds support for it adding the .coredump() driver callback.
> > As there is no longer a need to initiate it through debugfs remove
> > that code.
> >
> > Signed-off-by: Arend van Spriel <arend.vanspriel@xxxxxxxxxxxx>
> > ---
> >   drivers/net/wireless/marvell/mwifiex/debugfs.c | 31 +-------------------------
> >   drivers/net/wireless/marvell/mwifiex/pcie.c    | 19 ++++++++++++++--
> >   drivers/net/wireless/marvell/mwifiex/sdio.c    | 13 +++++++++++
> >   drivers/net/wireless/marvell/mwifiex/usb.c     | 14 ++++++++++++
> >   4 files changed, 45 insertions(+), 32 deletions(-)
>
> The documentation doesn't really say [1], but is the coredump supposed
> to happen synchronously? Because the mwifiex implementation is
> asynchronous, whereas it looks like the brcmfmac one is synchronous.

Well, that depends on the eye of the beholder I guess. From user-space 
perspective it is asynchronous regardless. A write access to the 
coredump sysfs file eventually results in a uevent when the devcoredump 
entry is created, ie. after driver has made a dev_coredump API call. 
Whether the driver does that synchronously or asynchronously is 
irrelevant as far as user-space is concerned.

> Brian
>
> [1] In fact, the ABI documentation really just describes kernel
> internals, rather than documenting any user-facing details, from what I
> can tell.

You are right. Clearly I did not reach the end my learning curve here. I 
assumed referring to the existing dev_coredump facility was sufficient, 
but maybe it is worth a patch to be more explicit and mention the uevent 
behavior. Also dev_coredump facility may be disabled upon which the 
trigger will have no effect in sysfs. In the kernel the data passed by 
the driver is simply freed by dev_coredump facility.

Regards,
Arend