On Wed, Apr 28, 2010 at 8:35 AM, rahul patil <[email protected]>
wrote:
>
> i want to call open,write system calls from kernel space.
>
[oops, didn't hit reply-to-all at first, sorry rahul!]
Not sure about open, but for read/write system calls, provided you already
have file opened and have the file descriptor, the following code snippets
should work:
For reads:
struct file *file = fget(fd)
if (file) {
loff_t pos = file_pos_read(file);
ret = vfs_read(file, buf, count, &pos);
file_pos_write(file, pos);
fput(file);
}
For writes:
struct file *file = fget(fd)
if (file) {
loff_t pos = file_pos_read(file);
ret = vfs_write(file, buf, count, &pos);
file_pos_write(file, pos);
fput(file);
}
No magic there, this is essentially the same code that gets executed when
you make read/write system calls defined in fs/read_write.c except that you
don't have to export sys_read and sys_write
Its a better idea to call file->f_op->read and file->f_op->write directly
instead of vfs_write in the above code, skips a lot of checks and stuff. See
how loop driver does this in drivers/block/loop.c in function
__do_lo_send_write.
You could even call write_begin and write_end directly if your backs fs
supports address space ops. Again good examples in loop driver.
HTH,
-Joel
