dumping large buffers to file

dumping large buffers to file

[Ramon Fried]

Hi.
I'm currently debugging a ISP DMA issue in a kernel module.
For debugging, I would like to dump buffers to a file on run time.
The buffers are quite big, 1MB at least.
As saving a file directly from kernel is discouraged, is there any available framework for doing such a thing ?
I can think of numerous ways of transferring the buffer to user space and saving it by a dedicated user process (Netlink, sysfs, char device, etc.)

I just don't want to invent the wheel. How do you do it ?

Thanks.
Ramon
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20151124/2f6caeec/attachment.html 

dumping large buffers to file

[Nick Krause]

On Tue, Nov 24, 2015 at 1:30 AM, Ramon Fried <ramon.fried@tandemg.com> wrote:
> Hi.
>
> I'm currently debugging a ISP DMA issue in a kernel module.
>
> For debugging, I would like to dump buffers to a file on run time.
>
> The buffers are quite big, 1MB at least.
>
> As saving a file directly from kernel is discouraged, is there any available
> framework for doing such a thing ?
>
> I can think of numerous ways of transferring the buffer to user space and
> saving it by a dedicated user process (Netlink, sysfs, char device, etc.)
>

>
> I just don't want to invent the wheel. How do you do it ?
>
>
>
> Thanks.
>
> Ramon
>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
If you can use printk just switch the log level to a log level that
prints to the syslog buffer
for kernel messages. If you have enough space on your partition for
root this shouldn't
be a problem, however if it is them I would recommend sysfs or procfs
exporting as
there better suited for debugging as the others are for user space
applications needing
access to kernel resources indirectly  or device driver user space interaction.
Hope this Helps,
Nick

dumping large buffers to file

[Valdis.Kletnieks at vt.edu]

On Tue, 24 Nov 2015 06:30:22 +0000, Ramon Fried said:

> I'm currently debugging a ISP DMA issue in a kernel module.
> For debugging, I would like to dump buffers to a file on run time.
> The buffers are quite big, 1MB at least.

The *other* question is how *often* you plan to do this.  Doing it
once a second is one thing, doing it once a millisecond is another.

> I can think of numerous ways of transferring the buffer to user space and
> saving it by a dedicated user process (Netlink, sysfs, char device, etc.)

sysfs is probably a bad choice due to its 'one attribute per file' rule,
debugfs would be a better approach.  netlink is probably an option, and
it's hard to argue with the simplicity of a char device with a plain
old 'tail -f /dev/my-debug-file > /tmp/debug.out' or similar...

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 848 bytes
Desc: not available
Url : http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20151124/eb0537a0/attachment.bin