Messages in this thread | | | Date | Sat, 25 Mar 2023 11:23:46 +0800 | Subject | Re: [PATCH 0/5]scsi:scsi_debug: Add error injection for single device | From | "haowenchao (C)" <> |
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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(+) >>>>>>> >>>>>> >>>>>> >>>>> >>>> >>> >>> >> > >
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