February 2011 - kernelnewbies@kernelnewbies.org

struct assignment?
by loody Feb. 19, 2011

Feb. 19, 2011

hi all: I found there seems no declaring about "struct ftrace_entry". below the greping result of my kernel source code: # grep -rwn 'struct ftrace_entry' * kernel/trace/trace.h:214: IF_ASSIGN(var, ent, struct ftrace_entry, TRACE_FN); \ kernel/trace/trace_events.c:1483: struct ftrace_entry *entry; kernel/trace/trace_output.c:818: struct ftrace_entry *field; kernel/trace/trace_output.c:845: struct ftrace_entry *field; kernel/trace/trace_output.c:859: struct ftrace_entry *field; kernel/trace/trace_output.c:872: struct ftrace_entry *field; kernel/trace/trace.c:1098: struct ftrace_entry *entry; # usually we use a struct we will declare its elements such as: struct usb_host_endpoint { struct usb_endpoint_descriptor desc; struct list_head urb_list; void *hcpriv; ...................... }; I guess the secret should be "if_assign", but how does compiler interpret it? -- Regards, miloody

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How to read data of specified disk block in ext2 ?
by kashish bhatia Feb. 19, 2011

Feb. 19, 2011

Hi All, Does anybody know a function which can be used to read the data of disk block in ext2 fs? -- Regards, Kashish

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Page table queries
by anish singh Feb. 19, 2011

Feb. 19, 2011

As i understood whenver a user space program is run it is represented in kernel using VMA which is managed by struct mm_struct and whenever the program is trying to read/write to a memory location in user space it will be directed to physical address using PAGE TABLE translation done by struct mm_struct(done in kernel space).Am i right? Suppose a simple driver wants the user to directly access its device memory then we use mmap.This mmap associates a set of user space virtual address with device driver memory and it is done by creating kernel page tables for the user space virtual addresses.Is the page table translation done everytime whenever user space does read/write to the device memory?? In .nopage function call we return the page associated with the physical address which the user wants to associate with user space virtual address.Is the page address returned by the nopage function same as seen by the user or will it be converted to user space virtual address(range between 0-2 GB)? Thanks for reading.

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Query regarding work queue
by Leelakrishna A Feb. 19, 2011

Feb. 19, 2011

Hi, In LDD 3rd edition it is given that, In a multiprocessor system work queues will run on the same processor from which they are submitted. Also each work queue has one or more dedicated kernel threads which runs the functions submitted to the queue. If we use *create_workqueue*, we get a work queue that has a dedicated thread for each processor on the system. If a work queue is restricted to run on one processor then why the need for the creation of more than one thread each for one processor. -Leela krishna

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some questions about kernel source
by loody Feb. 18, 2011

Feb. 18, 2011

Dear all: I have some questions about kernel source code: 1. in kernel/trace, I always see "__read_mostly" at the end of parameter is that a compiler optimization parameter? 2. what are below __releases and __acquires used for? ehci_urb_done(struct ehci_hcd *ehci, struct urb *urb, int status) __releases(ehci->lock) __acquires(ehci->lock) these 2 cmds are not in the {}, so I guess it will not compile out machine. If so, why we add them after function prototype? -- Regards,

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where can i find PCI rfc document
by prabhu Feb. 17, 2011

Feb. 17, 2011

Hi All, I am really interested to read about pci related information. I want PCI relared rfc document. I googled but i could not find the document. Please any one help me to get the document. Thanks, Prabhu

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Re: Interrupt handling
by Mulyadi Santosa Feb. 17, 2011

Feb. 17, 2011

Hi... :) On Tue, Feb 15, 2011 at 16:08, Darshan Ghumare <darshan.ghumare(a)gmail.com> wrote: > Sir, > On x86 UP (Single CPU), Can lower priority (say) IRQ5 preempt higher one > (say) IRQ4 (Currently, CPU is executing interrupt handler of IRQ4)? In Linux kernel, I never heard such irq prioritizing. Linux kernel does general preemption such that any code path could preempt other code path as long as preemption is allowed at that point and/or interrupt is enabled (which one affect the situation depends on type of code path). But, vaguely I read that Windows kernel does that.... that's why in certain BSOD you read message prefixed with "IRQL xxx xxx xxxx". That means lower interrupt handler somehow preempt higher one and that's not allowed. It comes from my raw observation so things might be wrong somewhere... -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

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some question about snprintf
by loody Feb. 17, 2011

Feb. 17, 2011

hi all: I want to use snprintf for collecting debug message and print it later. But I found : 1. when I add "\n" as below, the buffer will be cleared, that means the "irq status" will put at the head of Buffer instead of at the end of "ehci work". Size -= snprintf (Buffer , Size,"ehci_work\n"); Size -= snprintf (Buffer , Size,"irq status 0x%x\n",status); is it possible to add "\n" in the buffer, but will will not reset the buffer? 2. instead of snprintf, is there any better idea for saving debug message and show it out later? -- Regards, miloody

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I2C concept
by manikanta Feb. 17, 2011

Feb. 17, 2011

i2c_register_board_info- first parameter defines the bus number and this should match with the id for the device (which is resident on the I2C bus) while registering in board initialization files. AFAIK this bus number is basically an identifer to distinguish between different I2C bus drivers.Am i right?? If yes then in our platform we have only one I2C bus driver then why do we have to give different bus numbers?? Our devices are connected to different SDA and SCL lines(gpios basically) and for which we are using different bus numbers but we have common I2C driver. So why different bus numbers???

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iomem and ioports
by prabhu Feb. 17, 2011

Feb. 17, 2011

HI All, I started to understand output of /proc/oiports and /proc/iomem. I confused to relate these two's output. Below is the kernel source for Mapping of io-port to io-mem. Could anyone please explain below code. /* We encode the physical PIO addresses (0-0xffff) into the (0- * pointer by offsetting them with a constant (0x10000) and * assuming that all the low addresses are always PIO. That means means * we can do some sanity checks on the low bits, and don't * need to just take things for granted. */ #define PIO_OFFSET 0x10000UL #define PIO_MASK 0x0ffffUL #define PIO_RESERVED 0x40000UL void __iomem *ioport_map(unsigned long port, unsigned int nr) { __iomem if (port > PIO_MASK) return NULL; return (void __iomem *) (unsigned long) (port + PIO_OFFSET); __iomem } Thanks, Prabhu

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