Re: [PATCH 0/5]scsi:scsi_debug: Add error injection for single device

[haowenchao (C)]

On 2023/3/25 1:31, Douglas Gilbert wrote:
> On 2023-03-23 23:42, haowenchao (C) wrote:
> > On 2023/3/24 1:24, Douglas Gilbert wrote:
> > > On 2023-03-23 12:25, John Garry wrote:
> > > > On 23/03/2023 13:13, haowenchao (C) wrote:
> > > > > On 2023/3/23 20:40, John Garry wrote:
> > > > > > On 23/03/2023 11:55, Wenchao Hao wrote:
> > > > > > > The original error injection mechanism was based on scsi_host which
> > > > > > > could not inject fault for a single SCSI device.
> > > > > > >
> > > > > > > This patchset provides the ability to inject errors for a single
> > > > > > > SCSI device. Now we supports inject timeout errors, queuecommand
> > > > > > > errors, and hostbyte, driverbyte, statusbyte, and sense data for
> > > > > > > specific SCSI Command.
> > > > > >
> > > > > > There is already a basic mechanism to generate errors - like timeouts - on "nth" command. Can you say why you want this new interface? What special scenarios are you trying to test/validate (which could not be achieved based on the current mechanism)?
> > > > >
> > > > > I am testing a new error handle policy which is based on single scsi_device
> > > > > without set host to RECOVERY. So I need a method to generate errors for
> > > > > single SCSI devices.
> > > > >
> > > > > While we can not generate errors for single device with current mechanism
> > > > > because it is designed for host-wide error generation.
> > > > >
> > > > > > With this series we would have 2x methods to inject errors, which is less than ideal, and they seem to possibly conflict as well, e.g. I set timeout for nth command via current interface and then use the new interface to set timeout for some other cadence. What behavior to expect ...?
> > > > >
> > > > > I did not take this issue in consideration. I now assume the users would
> > > > > not use these 2 methods at same time.
> > > > >
> > > > > What's more, I don not know where to write the usage of this newly added
> > > > > interface, maybe we can explain these in doc?
> > > >
> > > > sysfs entries are described in Documentation/ABI, but please don't add elaborate programming interfaces in sysfs files (like in these patches) - a sysfs file should be just for reading or writing a single value
> > >
> > > Hi,
> > > Maybe this link might help for scsi_debug documentation:
> > >      https://doug-gilbert.github.io/scsi_debug.html
> > >
> > > And rather than sysfs for complicated, per (pseudo_ device
> > > settings, perhaps we could think about a SCSI mechanism like
> > > the "Unit Attention" mode page [0x0] which is vendor specific
> > > and used by Seagate and WDC for this sort of thing.
> > > A framework is already in the scsi_debug driver to change
> > > some mode page settings:
> > >
> > > # sdparm /dev/sg0
> > >      /dev/sg0: Linux     scsi_debug        0191
> > > Read write error recovery mode page:
> > >    AWRE          1  [cha: n, def:  1]
> > >    ARRE          1  [cha: n, def:  1]
> > >    PER           0  [cha: n, def:  0]
> > > Caching (SBC) mode page:
> > >    WCE           1  [cha: y, def:  1]
> > >    RCD           0  [cha: n, def:  0]
> > > Control mode page:
> > >    SWP           0  [cha: n, def:  0]
> > > Informational exceptions control mode page:
> > >    EWASC         0  [cha: n, def:  0]
> > >    DEXCPT        1  [cha: n, def:  1]
> > >    MRIE          0  [cha: y, def:  0]
> > >
> > > As can be seen WCE and MRIE are changeable, so
> > >
> > > # sdparm --clear=WCE /dev/sg0
> > > # sdparm --get=WCE /dev/sg0
> > >      /dev/sg0: Linux     scsi_debug        0191
> > > WCE           0  [cha: y, def:  1]
> > >
> > >
> > > Doug Gilbert
> >
> > Do you mean define scsi_debug's own format of mode page0(Vendor specific)
> > which contains these error injection info, and set/get these parameters
> > via sdparm?
> > If so, do we need to modify the sdparm code for these changes?
>
> Not a problem.
>
> > I want to add more injections in scsi_debug to test the SCSI middle layer,
> > for example, control return SUCCESS in scsi_debug_abort() or
> > scsi_debug_device_reset().
> >
> > These injections are more oriented to developers to trigger and observe
> > the error handler of SCSI middle layer.
> >
> > We can extend other error injections conveniently via my interface,
> > for example, add a new error code to add a new injection to control the
> > return value of scsi_debug_abort().
> >
> > If it's not recommended to add this interface in sysfs, what about proc? Like
> > /proc/scsi/scsi, we can write "scsi remove-single-device h:c:t:l" to manage
> > device.
>
> In the past, procfs has been used for this sort of thing
> but the powers that be want to phase that usage out.
>
> debugfs, even though it is usually mounted under sysfs at
> /sys/kernel/debug , does not seem to have the "one value
> per variable" restriction. So debugfs or configfs
> ( /sys/kernel/config ) might be better candidates.
> See 'df -ahT' .

Define scsi_debug's own format of mode page0 seems too complex and we have to
change the sdparm code. In order to make a better scalability, I prefer to add
these interface via debugfs. Actually, I design the format of the "error interface"
described in patch1 by referring to interfaces of ftrace.

The new interfaces based on debugfs would look like following:
/sys/kernel/debug/scsi_debug
	|
	+-- 0:0:0:1
	|	|
	|	\-- error
	|
	\-- 0:0:0:2
		|
		\-- error

> > > > > > I'm not saying that I am a huge fan of the current inject mechanism, but at the very least you need to provide more justification for this series.
> > > > > > > >
> > > > > > > The first patch add an sysfs interface to add and inquiry single
> > > > > > > device's error injection info; the second patch defined how to remove
> > > > > > > an injection which has been added. The following 3 patches use the
> > > > > > > injection info and generate the related error type.
> > > > > > >
> > > > > > > Wenchao Hao (5):
> > > > > > >    scsi:scsi_debug: Add sysfs interface to manage scsi devices' error
> > > > > > >      injection
> > > > > > >    scsi:scsi_debug: Define grammar to remove added error injection
> > > > > > >    scsi:scsi_debug: timeout command if the error is injected
> > > > > > >    scsi:scsi_debug: Return failed value if the error is injected
> > > > > > >    scsi:scsi_debug: set command's result and sense data if the error is
> > > > > > >      injected
> > > > > > >
> > > > > > >   drivers/scsi/scsi_debug.c | 296 ++++++++++++++++++++++++++++++++++++++
> > > > > > >   1 file changed, 296 insertions(+)