Re: help in block drivers

[Rahul <rahul.theraja@gmail.com>]

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On 10/20/06, Fawad Lateef <fawadlateef@gmail.com> wrote:
>
> Hello Rahul,
>
> First of all please don't do top-posting rather do bottom-posting. For
> more information search google.


oh sorry for that

On 10/19/06, Rahul Theraja <rahul.theraja@gmail.com> wrote:
> > Hello Shakthi Kannan,
> >
> >  Thanks for the reply .
> >
> >
> > > > driver. I could not understand why the "sbd_request " is called even
> > though
> > > > i have given only one read call from user space file.
> > >
> > > Block device I/O transfer is done in blocks.
> > >
> > > >  And also in the driver, in the function sbd_request() how does the
> > driver
> > > > get the parameters  like sector, current_nr_sectors and buffer.
> > >
> > > VFS <-> SCSI <-> Block device?
> > >
>
> I think its VFS<->Buffer-Cache<->Block-Device and if drive is mounted
> then VFS<->FS<->Buffer-Cache<->Block-Device
>
> > > > i could move
> > > > furhter fastly.
> > >
> > > Fastly? IMHO, learning kernel development involves lot of patience.
> > >
> > > SK
> >
> >
> >  Is it necessary to use kernel_thread() in block drivers.
> In  drivers/block
> > loop.c i could see  kernel_thread() being used but in floopy.c it is not
> > used. When is this kernel_thread() function is supposed to be used ?  In
> the
> > sbd_device also the kernel_thread() is not used.
> >
>
> First in kernel-2.6.x its better to use kthread_*() rather than
> kernel_thread if threading is needed.
>
> Threading isn't necessary in any device until unless you need it. For
> example if your driver is emulating a device or performing IO directly
> then you don't need it, but if your driver is sending request to a
> device which generates interrupts after completing IO and you want to
> do some extra work after getting IO completion interrupt then you must
> use thread. As threads work in process-context, hence can do sleep and
> lengthy processing but interrupt-context shouldn't sleep or nor do
> long processing.
>
> For getting more understanding about different contexts like process,
> interrupt, softirqs contexts do search google.
>
> >  Anyone please kindly clarify my doubts.
> >
>
> I hope you doubts are not clear.


thank you very much for all the help

>  Thanks in Advance
> >
> >  -Rahul
> >
>
> --
> Fawad Lateef
>

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