--- Shyamjith <shyamjithe@xxxxxxxxxxxxxxx> wrote:
> I know that this will work with 2.4.X kernel (not
> sure with 2.6). But
> usually its very dangerous to use this . because
> there is no proper locking
> mechanism while wrting to a file (i suppose ) . This
> may lead to
> inconsistancy .
do u mean that writing to a file in kernel, using
sys_write function can lead to inconsistency, i dont
think so. Its the top most function in system call
write and being the top most function it take care of
all things for file operation in kernel, so i think we
need not to worry about locking and unlocking of a
file.
When any application makes a system call write, this
function (sys_write) is dispacthed forom
sys_call_table to do all the write functionality.
I think its the best way to do file operations in
kernel by using top most function in kernel related to
file operations (like sys_open, sys_close, sys_read
.... etc)
All the top most functions in kernel which implements
the system calls start with "sys_" string in front. I
tried using sys_kill in kernel mode to send signal to
some process and it works fine.
Yes definitely this puts some overhead, as we call the
top most function.
--gd
>
>
> ----- Original Message -----
> From: "Amith" <amith@xxxxxxxxxxxxxxx>
> To: "shyamjith" <shyamjithe@xxxxxxxxxxxxxxx>
> Cc: <kernelnewbies@xxxxxxxxxxxx>; "Jan Hudec"
> <bulb@xxxxxx>
> Sent: Wednesday, February 02, 2005 2:58 PM
> Subject: Re: How to read file in kernel module?
>
>
> > shyamjith wrote:
> >
> > > When u register a device with the kernel for
> example, a character device
> > > U attach the device structure into the device
> table . which is filled
> > > with
> > > pointers to our read and write functions .while
> registering a proc
> > > entry also we can fill such functional pointers
> .
> > >
> > > up up and away
> > >
> > > shyam
> >
> > ok , so u mean the file_operat ions table.
> >
> >
> > >
> > >See i think we are talking about kernel
> programming . What i mean to say
> is
> > >that there is only two ways to communiacte to
> user space . One through a
> > >registerd read or write functions & other one
> through proc file system .
> > >
> >
> > Well, what about the code below ? i know it's not
> an accepted way of doing
> it , but it sure beats your
> > *only* 2 ways of doing it :-) !
> >
> > < kfs.c >
> > int
> > kopen(const char *filename,int flags)
> > {
> > oldmm = get_fs();
> > set_fs(get_ds());
> > kfd = sys_open(filename,flags |
> O_CREAT,S_IRWXU);
> > if(kfd > 0) {
> > printk("<1>kfd = %d \n",kfd);
> > set_fs(oldmm);
> > return kfd;
> > }
> > return kfd;
> > }
> >
> >
> > int
> > kwrite(int fd,char *buffer,int size)
> > {
> > int red;
> > oldmm = get_fs();
> > set_fs(get_ds());
> > red = sys_write(fd,write_buffer,size);
> > if(red > 0) {
> > printk("<1>write buffer = %s \n",write_buffer);
> > set_fs(oldmm);
> > return red;
> > }
> > }
> >
> >
> > i had written this code sometime ago and it did
> work !
> >
> > cheers,
> > Amith
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
> --
> Kernelnewbies: Help each other learn about the Linux
> kernel.
> Archive:
> http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
>
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