On Monday 07 February 2005 18:46, Joerg Hoh wrote:
> Hi
>
> I have a problem regarding a procfs entry.
>
> I created one and added a read_func. If I do a
> "cat /proc/.../my_entry", debug-printk's show me, that my read function is
> called 3 times. It returns 21,19 and 21 bytes.
>
> A "strace cat /proc/.../my_entry" has the following output
>
> ...
> open("/proc/.../my_entry") = 3
> ...
> read(3,"21 bytes output ...",4096) = 21
> write(1,"21 bytes output ...") = 21
> read(3,"",4096) = 0
> ...
> close(3)
>
>
> I have no clue what happens. My module shows me 3 calls of the read function,
> but strace shows only 2 (and a return value which is never returned from the
> read function). Can anyone explain me what happens here?
You never set 'start'. It is a pointer into 'page' corresponding to the
offset, 'off' in the virtual file that the read is trying to resolve.
I believe you are misusing 'off'. It is the offset into the virtual
file - not the offset into 'page'. snprintf() might return -1. Looks
like you are doing bad things with the semaphore as well. I don't think
you can assume your routine will get called until EOF.
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