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Customizing UIO mmap'ing
by Kenneth Adam Miller Dec. 18, 2015

Dec. 18, 2015

So, previously I think I misunderstood how to use uio_dmem_genirq. Let me explain the way I think it currently works (bare with me, I departed from looking at this driver after only about a week of looking at it): Generally uio_dmem_genirq.c builds on top of uio.c, which provides a common module basis for isolating code common to the other specific modules. But for a specific purpose, uio_dmem_genirq.c has be either customized or extended in order that specific memory regions can be set as accessible. Most easily, this is done in a first come first serve approach by filling out the details (which exactly?) left missing in uio_dmem_genirq.c, and to start, that would be in uio_of_genirq_match <https://proxy-us.hide.me/go.php?u=zWvu%2Fc4k0RUgdQesK%2F26T4EuwcXktyOuOa%2F…> . Am I correct?

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Track execution of close() system call in kernel
by Harsh Jain Dec. 18, 2015

Dec. 18, 2015

Hi, How to track the code flow of close() system call for socket fds. In working case I am getting following debug traces in dmesg inet_release sk ffff88040e376000 sk->sk_prot->close ffffffffa0774a50 chelsio_close Entered CPU: 3 PID: 10108 Comm: openssl Tainted: G O 3.17.8_harsh_cry_test_dis #28 Hardware name: Supermicro X8ST3/X8ST3, BIOS 2.0 07/29/10 0000000000000000 ffff8800d87ebde8 ffffffff815e8356 ffffffff81dc21a0 ffff88040e376000 ffff8800d87ebe28 ffffffffa0774a91 ffff88040646f880 ffff88040e376000 0000000000000000 ffff8803fef299c0 ffff8803fef299f0 Call Trace: [<ffffffff815e8356>] dump_stack+0x51/0x6b [<ffffffffa0774a91>] chelsio_close+0x41/0x340 [t4_tom] [<ffffffff815966c0>] inet_release+0xc0/0xd0 [<ffffffff815030b9>] sock_release+0x29/0xa0 [<ffffffff81503582>] sock_close+0x12/0x20 [<ffffffff811bf1b0>] __fput+0xd0/0x260 [<ffffffff811bf3ee>] ____fput+0xe/0x10 [<ffffffff81089e5d>] task_work_run+0xad/0xe0 [<ffffffff81003d74>] do_notify_resume+0x84/0x90 [<ffffffff815ed8da>] int_signal+0x12/0x17 chelsio_close Exit After doing changes in kernel module dumpstack is not getting printed from "chelsio_close" function. I added function entry/exit trace in "sock_release" also. Return value of close() system call is also zero. Its executing successfully but where in kernel code? Regards Harsh Jain

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Work with correct branch for kernel changes
by Shirish Gajera Dec. 17, 2015

Dec. 17, 2015

Hi, I am new to linux kernel and trying to understand the process of different git branch to work. So, if I am not wrong then there are different branch like stable, next, staging etc. Previously I work with staging branch so if I am making any changes for drivers/staging I have to work with staging branch like follow. git clone git checkout -t -b staging-testing origin/staging-testing git chekcout -b MY_LOCAL_BRANCH not do work and subimt So, how it work for other source structure, like now I want to make some for y2038 -> drivers/scsi which branch should I set up and work with, next/stable/or is there any specific y2038 branch. Any wiki link or documentation that explain this full process which branch to work with when making changes to specific directory will be useful. Thanks, Shirish

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Query on freeing of new_fdt->open_fds inside src/fs/file.c
by pavi1729 Dec. 11, 2015

Dec. 11, 2015

Hi, I am unable to understand how new_fdt->open_fds can be freed in __free_fdtable when its an unsigned long in files_struct ? Details: FUNCTION: dup_fd http://lxr.free-electrons.com/source/fs/file.c#L261 LINE : 282 : new_fdt->open_fds = newf->open_fds_init; files_struct : http://lxr.free-electrons.com/source/include/linux/fdtable.h#L45 unsigned long open_fds_init[1]; Cheers, Pavi

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Ftrace: tracing init call of out of tree modules
by Jay Aurabind Dec. 11, 2015

Dec. 11, 2015

Hi, I am learning ftrace. I would like to know to use frace filters for tracing a module's init function. For example, assume the module uvcvideo. While the module is loaded, cat available_filter_functions | grep uvcvideo will give me a big list of functions. Then I enable those functions by setting ftrace filter with: echo "uvc*" > set_ftrace_filter However, as soon as I rmmod the driver, set_ftrace_filter becomes empty automatically. So how do I do a trace on out-of-tree modules I have ? -- Thanks and Regards, Aurabindo J

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Fwd: objdiff
by sasa bogicevic Dec. 10, 2015

Dec. 10, 2015

> Hi All, > I am trying to prove that my changes in code in complete drivers/pci/hotplug folder didn’t brake anything so I: > get the staging-testing tree > compile just drivers/pci/hotplug folder > use ./scripts/objdiff record drivers/pci/hotplug > make changes > commit > compile again just that folder > record again with objdiff > and when I do ./scripts/objdiff diff commit1 commit2 I get no output. > Is this normal? How do I prove all compiles normally ? { name: Bogicevic Sasa phone: +381606006200 }

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What is the return value of test_bit() in <asm/bitops.h> on x86_64?
by Le Tan Dec. 10, 2015

Dec. 10, 2015

Hi, I was shocked when I found that `test_bit()` will return -1 or 0 to denote whether a bit is set or not in a bitmap. Looking at its implementation here: ``` static __always_inline int constant_test_bit(long nr, const volatile unsigned long *addr) { return ((1UL << (nr & (BITS_PER_LONG-1))) & (addr[nr >> _BITOPS_LONG_SHIFT])) != 0; } static inline int variable_test_bit(long nr, volatile const unsigned long *addr) { int oldbit; asm volatile("bt %2,%1\n\t" "sbb %0,%0" : "=r" (oldbit) : "m" (*(unsigned long *)addr), "Ir" (nr)); return oldbit; } ``` The sbb instruction will let `det = dst - (src + CF)`. So it seems that test_bit() will return -1 if a bit is set? And it seems to work that way in my project. However, when I wrote another toy function to test it, I saw that it will return 1 for those bits set. ``` #define TEST_MAX_BITS 512 static void rr_unit_test(struct kvm_vcpu *vcpu) { static u64 counter = 0; int ret; DECLARE_BITMAP(test_map, TEST_MAX_BITS); u64 nr; if (vcpu->vcpu_id != 0) return; if (counter == 0) { ++counter; bitmap_zero(test_map, TEST_MAX_BITS); ret = test_bit(5, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); set_bit(5, test_map); ret = test_bit(5, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); ret = test_bit(6, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); ret = test_bit(512, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); set_bit(512, test_map); ret = test_bit(512, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); nr = 448; ret = test_bit(nr, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); set_bit(nr, test_map); ret = test_bit(nr, test_map); printk(KERN_INFO "vcpu=%d ret=%d\n", vcpu->vcpu_id, ret); } } ``` So why will test_bit() behave differently? Thanks very much! Regards, Le Tan

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Tracing built-in drivers ?
by Jay Aurabind Dec. 9, 2015

Dec. 9, 2015

Hi, I know I can use ftrace or perf to do tracing on modules that I can load from the userspace. But what if I want to do tracing on a driver which is built in ? For example, i915. There wouldnt be any userspace to trigger a trace when it does an init. Even if I recompile i915 as a module, I am not able to unload it. Are there any specific tools or techniques for doing this ? -- Thanks and Regards, Aurabindo J

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What are the differences between the -next tree and the -mm tree?
by Hao Lee Dec. 9, 2015

Dec. 9, 2015

Hi, I'm sorry to bother you to ask some questions about -next tree and -mm tree. I have read some documents about kernel trees, but I don't know the difference between the -next tree and -mm tree. In this post: http://lists.kernelnewbies.org/pipermail/kernelnewbies/2013-October/009145.… It seems that the -mm tree has been substituted by the -next tree. Besides, I can't find -mm tree in anywhere. So, could you explain the difference between the two trees. Regards, HaoLee

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if i want powerpc "local bus" support, must i select CONFIG_FSL_LBC?
by Robert P. J. Day Dec. 7, 2015

Dec. 7, 2015

trying to make a long story short, was handed an aging powerpc MPC8360e system on which to place linux, along with a BSP that does in fact generate a bootable kernel and filesystem. however, according to this online page (and i am *not* in any way a powerpc expert): http://cache.freescale.com/files/netcomm/doc/fact_sheet/MPC8360EFS.pdf this processor has something called a "local bus", off of which on this board hang things like DSP, FPGA and other things. during boot, i can see absolutely no mention of any of the devices attached to this local bus, or even that the bus itself is recognized, then i noticed that the .config file used to build this 3.14.29 kernel does not select what looks like the appropriate kernel option FSL_LBC. if anyone out there is a powerpc expert, can you confirm that you need to select that option (and hence compile in the source file arch/powerpc/sysdev/fsl_lbc.c) to get that support? i'm puzzled only because, if that file is required for local bus support, the people who gave us the BSP really should have turned it on. thanks for any guidance. rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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