May 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Fwd: how to debug kernel in qemu using ubuntu image
by Amirali Shambayati May 16, 2011

May 16, 2011

---------- Forwarded message ---------- From: Amirali Shambayati <amirali.shambayati(a)gmail.com> Date: Tue, May 10, 2011 at 3:11 PM Subject: how to debug kernel in qemu using ubuntu image To: Linux Kernel <linux-kernel(a)vger.kernel.org> Hello all, I asked my question in "linux kernel" mailing list, and I was suggested to forward it to this mailing list. I'm using linux-0.2.img image(which is a light linux image) to debug kernel using Qemu. I'm working on IO schedulers' optimization. As Qemu boots kernel, IO scheduler sends read requests to disk. Also by entering commands such as 'ls', it sends read requests. I'm looking for a way to send write requests. Thus I thought that using a benchmark which sends both read and write requests, is suitable, but as linux-0.2.img is a very simple and light image, it is almost impossible to setup heavy benchmarks on it. So I want to use an ubuntu image instead. But I don't know where I should see kernel printks. Thanks in advance Regards, -- Amirali Shambayati Bachelor Student Computer Engineering Department Sharif University of Technology Tehran, Iran -- Amirali Shambayati Bachelor Student Computer Engineering Department Sharif University of Technology Tehran, Iran

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Regarding IRQF_DISABLED replacement.
by mindentropy May 16, 2011

May 16, 2011

Hi, What is the replacement for IRQF_DISABLED as its simply a noop and will be deprecated soon? I was going through my floppy controller code and I am not sure what to use. Thanks.

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Re: Fwd: how to debug kernel in qemu using ubuntu image
by Vikram Narayanan May 16, 2011

May 16, 2011

> Hello all, > > I asked my question in "linux kernel" mailing list, and I was > suggested to forward it to this mailing list. > > I'm using linux-0.2.img image(which is a light linux image) to debug > kernel using Qemu. I'm working on IO schedulers' optimization. As Qemu > boots kernel, IO scheduler sends read requests to disk. Also by > entering commands such as 'ls', it sends read requests. I'm looking > for a way to send write requests. Thus I thought that using a > benchmark which sends both read and write requests, is suitable, but > as linux-0.2.img is a very simple and light image, it is almost > impossible to setup heavy benchmarks on it. So I want to use an ubuntu > image instead. But I don't know where I should see kernel printks. kernel printk's can be seen from the dmesg output. Just type dmesg in your shell. You can also see that in /var/log/syslog Hope it helps, Vikram

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Network packet processing related Query
by Sachin Rane May 16, 2011

May 16, 2011

--------- Resending the same query as nobody responded to the previous attempt ------ Hi, I want to improve my understanding about the logic of the code written for 'process_backlog ()' . File Source: net/core/dev.c, linux-2.6.16 I am considering only Non-NAPI network devices ( > 1) in this discussion. The 'net_rx_action' function invokes 'dev->poll(dev, &budget)' for each network device present in 'poll_list'. ' The default handler for Non-NAPI network devices is 'process_backlog ()'. The signature of the function is: static int process_backlog (struct net_device *backlog_dev, int *budget) 'backlog_dev' represents the device for which the 'poll' function is invoked. In the code body the function acts on CPU specific 'input_pkt_queue'. This queue holds all the incoming packets from the network devices and 'poll_list' has reference for these network devices. The function takes out one element (packet) from the 'input_pkt_queue' and process the packet. As the 'input_pkt_queue' is shared by all the network devices, the 'packet' which is popped-out from the list can be from any network device not required to be from 'backlog_dev' (the device for which 'process_backlog' has been called). I have confusion here. The code doesn't operate only on the packets queued-in by 'backlog_dev' to 'input_pkt_queue'. It pops-out the node from the queue and process it. But it updates the 'quota' which is specific for the device 'backlog_dev' for which the function have got called. Why it is so? Am I missing out something here? Thanks for reading my mail patiently. Regards, Sachin Rane

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kernel BUG while reading from SPI into static buffer
by Felix Varghese May 16, 2011

May 16, 2011

Hi, I am trying to read some data via SPI on an a modified (custom SPI device attached) AT91SAM9G20-EK board. If I pass a local array buffer, declared as "char buffer[100];" as the rx_buf pointer for the spi transfer, the code works fine. But if I just change the declaration to "static char buffer[100]" instead, I get the following crash: kernel BUG at arch/arm/mm/dma-mapping.c:425! Unable to handle kernel NULL pointer dereference at virtual address 00000000 pgd = c0004000 [00000000] *pgd=00000000 Internal error: Oops: 817 [#1] last sysfs file: Modules linked in: testmod [last unloaded: testmod] CPU: 0 Not tainted (2.6.37.2 #8) PC is at __bug+0x1c/0x28 LR is at __bug+0x18/0x28 pc : [<c0031d88>] lr : [<c0031d84>] psr: 20000093 sp : c3a6fea8 ip : 00001e7b fp : 00000000 r10: ffffffff r9 : 00000000 r8 : c38ca6a0 r7 : c395e4e8 r6 : c3a6ff28 r5 : 00000032 r4 : c3a6ff54 r3 : 00000000 r2 : 00000001 r1 : 60000093 r0 : 00000033 Flags: nzCv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel Control: 0005317f Table: 23a3c000 DAC: 00000017 Process tx_thread (pid: 460, stack limit = 0xc3a6e270) Stack: (0xc3a6fea8 to 0xc3a70000) fea0: c3a6ff24 c0034344 c0274848 c3a6ff54 bf00c7f8 c0189dd4 fec0: c395e4e8 60000013 c3a6ff28 c395e400 c395e400 00000000 00000000 c0188bf0 fee0: c3a6ff2c 60000013 c3a6ff28 c395e400 c38ca6a0 c0188c54 c3a6ff04 c0188e38 ff00: 00000000 00000000 c3a6ff08 c3a6ff08 c3a6ff94 c3a6ff70 c3a6ff28 bf00c7f8 ff20: 00000032 bf00a0d4 c3a6ff94 c3a6ff70 c38ca6a0 00000000 c0188fdc c3a6ff04 ff40: 00000000 ffffff8d 00000000 00000000 00000000 00000000 bf00c7f8 00000032 ff60: ffffffff ffffffff 00000000 00000000 c3a6ff28 c3a6ff94 c3a6ff9f c3a6ff9f ff80: 00000001 23a6ff9f 23a6ff9f 00000000 00000000 c3a6ff70 c3a6ff28 20a6ff50 ffa0: c3a6ffd4 c39bfdc4 c38ca6a0 bf00a0e0 00000000 bf00a168 720a0000 01a6cafe ffc0: c3a6ffd4 c00556e0 c002f884 00000000 c38ca6a0 00000000 c3a6ffd8 c3a6ffd8 ffe0: 00000000 c39bfdc4 c0055660 c002f884 00000013 c002f884 0001151c 000000d0 [<c0031d88>] (__bug+0x1c/0x28) from [<c0034344>] (___dma_single_cpu_to_dev+0x3c/0x68) [<c0034344>] (___dma_single_cpu_to_dev+0x3c/0x68) from [<c0189dd4>] (atmel_spi_transfer+0xf8/0x1cc) [<c0189dd4>] (atmel_spi_transfer+0xf8/0x1cc) from [<c0188bf0>] (__spi_async+0xa0/0xb0) [<c0188bf0>] (__spi_async+0xa0/0xb0) from [<c0188c54>] (spi_async_locked+0x14/0x2c) [<c0188c54>] (spi_async_locked+0x14/0x2c) from [<c0188e38>] (__spi_sync+0x60/0xa0) [<c0188e38>] (__spi_sync+0x60/0xa0) from [<bf00a0d4>] (read_bytes+0xac/0xb8 [testmod]) [<bf00a0d4>] (read_bytes+0xac/0xb8 [testmod]) from [<bf00a168>] (tx_thread+0x88/0x110 [testmod]) [<bf00a168>] (tx_thread+0x88/0x110 [testmod]) from [<c00556e0>] (kthread+0x80/0x88) [<c00556e0>] (kthread+0x80/0x88) from [<c002f884>] (kernel_thread_exit+0x0/0x8) Code: e1a01000 e59f000c eb090854 e3a03000 (e5833000) ---[ end trace 0dac538caa941b38 ]--- Does this behaviour make sense to anyone? Is this a bug or is it just me doing the wrong thing? Regards, Felix.

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How vmlinux is recognized?
by Vikram Narayanan May 16, 2011

May 16, 2011

Hi, Sorry if this question is stupid. How the vmlinux (an ELF executable) is recognized by the processor? What are the files that are responsible for this? Thanks, Vikram

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is the tickless kernel now the "standard"?
by Robert P. J. Day May 16, 2011

May 16, 2011

given that ubuntu ships with the kernel configured for tickless behaviour, and that RHEL6 also ships tickless, is it safe to say that tickless is now the standard configuration? is there a compelling reason to *not* run tickless with the latest 2.6 kernels? 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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asm/types.h question
by Ezequiel García May 16, 2011

May 16, 2011

Hi all, The types listed in <asm/types.h> __u8, __u16, __u32 and such... ¿ are these types the same as the ones for the kernel ?

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should drivers avoid the use of in_atomic()?
by Robert P. J. Day May 15, 2011

May 15, 2011

perusing some timer-related kernel stuff and i ran across this in include/linux/hardirq.h: /* * Are we running in atomic context? WARNING: this macro cannot * always detect atomic context; in particular, it cannot know about * held spinlocks in non-preemptible kernels. Thus it should not be * used in the general case to determine whether sleeping is possible. * Do not use in_atomic() in driver code. */ #define in_atomic() ((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_INATOMIC_BASE) but a quick check shows a sprinkling of in_atomic() checks in the drivers/ directory. is that admonition overly strict? or what? 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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rtc_ops structure
by Vikram Narayanan May 14, 2011

May 14, 2011

Hi, Is the structure rtc_ops still used in rtc drivers in the new kernels? If not, what is the equivalent of it? Thanks, Vikram

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