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ALIGN MACRO understanding
by sdptroy3＠gmail.com Nov. 8, 2013

Nov. 8, 2013

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Re: scsi subsystem in linux
by pmkernel Nov. 8, 2013

Nov. 8, 2013

I think sd_prep_fn is a generic function for any SCSI device while scsi_prep_fn specifically SCSI Disks or LUN's, so if you have a filesystem created on top of SCSI Disk scsi_prep_fn function will be called. In case you have any other SCSI device then you will have sd_prep_fn will be called. The comment on top of sd_probe mentions this: /** * sd_probe - called during driver initialization and whenever a * new scsi device is attached to the system. It is called once * for each scsi device (not just disks) present. * @dev: pointer to device object Similarly argument to scsi_alloc_sdev ( while internally calls scsi_alloc_queue ---> blk_queue_prep_rq(q, scsi_prep_fn) ) accepts lun id which I think is specific to SCSI LUN. For understanding linux SCSI Subsystem you can also refer to kernel SCSI documentation and also the below mentioned link: http://www.andante.org/scsidoc/SCSI-1.html Regards, Piyush Moghe -------- Original message -------- From: Jack Wang <xjtuwjp(a)gmail.com> Date: To: nidhi mittal hada <nidhimittal19(a)gmail.com> Cc: Kernelnewbies <kernelnewbies(a)nl.linux.org>,"rohan.puri.15" <rohan.puri.15(a)gmail.com>,sumeetgandhare <sumeetgandhare(a)gmail.com>,kernelnewbies@kernelnewbies.org Subject: Re: scsi subsystem in linux On 11/05/2013 05:19 PM, nidhi mittal hada wrote: > My doubt is :- > When we know block device driver , request structure, request queue > operation .. as per LDD. > How and where the request structure we are getting in scsi layer > fits/relates to thi sblock layer request structure.... > > is the sequence ..block device layer request function -> calls scsi > layer request function ? > > The links below show how block layer request connect to scsi request, but In Chinese, sorry, but you may find clue in the code section. http://blog.csdn.net/fudan_abc/article/details/1966510 http://blog.csdn.net/fudan_abc/article/details/1966538 http://blog.csdn.net/fudan_abc/article/details/1967045 http://blog.csdn.net/fudan_abc/article/details/1967050 BTW: Why not use dm-crypt? Jack > > > > > > On Tue, Nov 5, 2013 at 6:34 PM, nidhi mittal hada > <nidhimittal19(a)gmail.com <mailto:nidhimittal19@gmail.com>> wrote: > > _*Setting of sd_prep_fn()*_ > sd_probe is called*/whenever a/* */new scsi device is attached to > the system. /* > > sd_probe calls -> sd_probe_async-> > inside sd_probe_async, request prep fn is set to *sd_prep_fn* > >>>>like this blk_queue_prep_rq(sdp->request_queue, sd_prep_fn); > > > _*Calling of sd_prep_fn*_ > ????? > > Is this request queue sdp->request_queue, different from the request > queue, > for which scsi_prep_fn is used?? > > Are they on different layers ? > > Is there some relation between them ? > > > > Thanks > Nidhi > > > On Tue, Nov 5, 2013 at 6:13 PM, nidhi mittal hada > <nidhimittal19(a)gmail.com <mailto:nidhimittal19@gmail.com>> wrote: > > scsi_alloc_sdev(must be called once for each scsi device) -->calls > scsi_alloc_queue (that sets up sdev->request_queue > sets up scsi_request_fn and > sets up req prep function as > scsi_prep_fn) > > 1738 struct request_queue *scsi_alloc_queue(struct scsi_device > *sdev) > 1739 { > 1740 struct request_queue *q; > 1742 q = __scsi_alloc_queue(sdev->host, > scsi_request_fn);>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > 1743 if (!q) > 1744 return NULL; > 1746 blk_queue_prep_rq(q, > scsi_prep_fn);>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > 1747 blk_queue_softirq_done(q, scsi_softirq_done); > 1748 blk_queue_rq_timed_out(q, scsi_times_out); > 1749 blk_queue_lld_busy(q, scsi_lld_busy); > 1750 return q; > 1751 } > And after this call sdev_request_queue is allocated................ > > Now, scsi_request_fn should be called while processing each > request in this sdev->request_queue... > Please correct me if i m wrong. > Now, inside scsi_request_fn, we get next queueable request by > calling > blk_peek_request - to fetch request from request queue .. > > blk_peek_request -> calls __elv_next_request to fetch next request- > and calls prep_rq_fn(q, rq); > > > *which is scsi_prep_fn not the sd_prep_fn isnt it ??* > > > Then where is sd_prep_fn is used for ?? > > Thanks > Nidhi > > > > > On Tue, Nov 5, 2013 at 5:39 PM, Jack Wang <xjtuwjp(a)gmail.com > <mailto:xjtuwjp@gmail.com>> wrote: > > Hi Nidhi, > > About the function call trace you can use ftrace to find > out, another > useful tool is scsi_logging_level to set more verbose > logging output for > scsi core. > > Regards > Jack > On 11/05/2013 12:48 PM, nidhi mittal hada wrote: > > > > Hi All > > > > i have got a requirement where I need to encrypt/decrypt > data that goes > > from scsi layer to a particular block device. > > As per my understanding till now on scsi subsystem in > linux, i think i > > need to > > use crypto api and call appropriate encrypt/decrypt > function from sd > > driver for block device. > > > > I need to locate that specific function where this change > needs to be > > made ... > > I know basic block device driver writing in linux .. But > not able to fit > > scsi in this picture. > > > > I have few basic doubts.. kindly help in resolving ... > > > > 1) Now, as example block device driver sbull, as given > LDD, works on > > request queue, fetches req from this queue, using function > req = > > elv_next_request(q)), > > in request function. > > what is corresponding function in sd layer ? > > That is the function where i have req->buffer in hand with > me.. > > > > > > 2) For a write operation from initiator to disk > > is the hierarchy like this > > *sd_prep_fn* > > generic block device request structure -> converted into > scsi specific > > request structure > > OR > > what is scsi_prep_fn for?? > > > > 3)How is Scpnt pointer that is req-> special is used in > sd_prep_func.. > > is processed? i mean which layer picks Scpnt up and > processes ?? > > > > 4)Any document any URL any kind of instruction will be > extremely helpful. > > > > 5)Whenever a *new scsi device is attached *sd_probe is called > > sd_async_probe() is the async part of sd_probe() So when > this is called > > the prep_fn is set to sd_prep_fn and hence this will be > called. > > > > *But i thought sd_prep_fn should be called for each and > every request > > .....??* > > Kindly help me to clear the confusion .. > > > > > > Thanks > > Nidhi > > > > > > > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies(a)kernelnewbies.org > <mailto:Kernelnewbies@kernelnewbies.org> > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > > > > > > > > -- > Thanks & Regards > Nidhi Mittal Hada > > http://nidhi-searchingmyself.blogspot.com/ > > > > > -- > Thanks & Regards > Nidhi Mittal Hada > > http://nidhi-searchingmyself.blogspot.com/ > _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Kernel_project_Idea
by Anup Buchke Nov. 8, 2013

Nov. 8, 2013

Hi all, I have to do a small kernel-level project in OS course at my school. Broadly, they have told us to do project in areas Linux Memory Managment/ Linux Process management. Any ideas? Some of which I thought were:: Linux MM: Some small project involving use of DMA kernel API,or getting the number of pages for a process and its details, or something similar.... Linux process management: trying to access linux runqueue and maintaining some information...or looping through process descriptor list and accessing some info...etc. It is difficult for me to come up with some precise project idea which can be completed in 10-15 days. So it would be great if anyone can help me define some project which can be completed in that time. *My background:* I have done basic device driver programming,aware of kernel synchronization techniques,kernel allocation techniques,have understood and used tasklets,workqueue. Good understanding of OS concepts. Thanks Anup Buchke

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Why I can't mount usb stick with my uid or gid?
by 乃宏周 Nov. 7, 2013

Nov. 7, 2013

I use ubuntu 12.04, and my usb stick had been found at /dev/sdb and has 2 partitions. If I `mount /dev/sdb1 ~/work`, My usb stick can be mounted sucessfully, but ownership of ~/work is root, so I can't write anything to it. But if I `mount -o uid=1000,gid=1000 /dev/sdb1 ~/work`, system replies following error message: mount: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so Why this situation occurred? I'm sure that my pid and gid is 1000. Any ideas?

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scsi subsystem in linux
by nidhi mittal hada Nov. 7, 2013

Nov. 7, 2013

Hi All i have got a requirement where I need to encrypt/decrypt data that goes from scsi layer to a particular block device. As per my understanding till now on scsi subsystem in linux, i think i need to use crypto api and call appropriate encrypt/decrypt function from sd driver for block device. I need to locate that specific function where this change needs to be made ... I know basic block device driver writing in linux .. But not able to fit scsi in this picture. I have few basic doubts.. kindly help in resolving ... 1) Now, as example block device driver sbull, as given LDD, works on request queue, fetches req from this queue, using function req = elv_next_request(q)), in request function. what is corresponding function in sd layer ? That is the function where i have req->buffer in hand with me.. 2) For a write operation from initiator to disk is the hierarchy like this *sd_prep_fn* generic block device request structure -> converted into scsi specific request structure OR what is scsi_prep_fn for?? 3)How is Scpnt pointer that is req-> special is used in sd_prep_func.. is processed? i mean which layer picks Scpnt up and processes ?? 4)Any document any URL any kind of instruction will be extremely helpful. 5)Whenever a *new scsi device is attached *sd_probe is called sd_async_probe() is the async part of sd_probe() So when this is called the prep_fn is set to sd_prep_fn and hence this will be called. *But i thought sd_prep_fn should be called for each and every request .....??* Kindly help me to clear the confusion .. Thanks Nidhi

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GIt Checkout of Kernel Repo
by Arun M Kumar Nov. 6, 2013

Nov. 6, 2013

I have recently cloned the GIT repo of the Kernel Source. the remote being set as origin git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git (fetch) origin git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git (push) now according to www.Kernelnewbies.org/KernelBuild git tag -l | less would list out all the tags associated with a build including the release candidates... But I am getting tags ONLY till v3.9.9 has there been a change of some kind? or is there an issue on my side?

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Packet loss in a bridge
by Anil Joshi Nov. 6, 2013

Nov. 6, 2013

Hi All, I have created a bridge on two nics on the same machine. The machine having a bridge is an intermediate machine to send packets across network. I am seeing much packet loss in the intermediate machine (i think due to bridge "brctl") How to avoid it? Thanks Anil

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Festival Shutdown : Kernelnewbies Digest, Vol 36, Issue 10
by hemal.patel＠slscorp.com Nov. 6, 2013

Nov. 6, 2013

Hi, Due to Diwali Festival, SLS will be closed from Oct. 31th to Nov. 6th. We will return on Nov. 7th to the office. For urgent matter please call on 001-408-852-0067. For more information about Diwali: http://en.wikipedia.org/wiki/Diwali Regards, Hemal Patel

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How to prevent other processes from being scheduled
by J.Hwan Kim Nov. 6, 2013

Nov. 6, 2013

Hi, everyone How can I prevent other processes than my specific application from being scheduled? I thougt that when my program being started, it would invokes the kernel to do "local_irq_disable()" and when it ended, it would call "local_irq_enable()" in order that scheduler not working when my specific program runs. But i seems do not work as I likes. Please give me some hints what i should do... Thanks in advance. J.Hwan Kim

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GDB usage
by Anil Joshi Nov. 6, 2013

Nov. 6, 2013

Hi All, I am all new Linux and I was trying to read Snort (http://www.snort.org/) . The best way to read it is through GDB debugger. The problem that i am facing is : 1> It has so many files i don't know where is the start function,how to find out that? 2> how to put the complete software in gdb,Please guide. Thanks Anil

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