On Tue, Apr 29, 2003 at 01:15:29PM -0700, Ahmed A wrote:
>
> Hello,
>
> I am using the following like to open /dev/sda (I am
> guessing this is called a raw device).
>
>
> fd = open ("/dev/sda", O_RDWR | O_SYNC | O_DIRECT);
>
> I have a few questions regarding the above:
>
> 1. Can I use O_DIRECT while opening the device? Will
> it have any effect. Or do I need to go through a file
> system (which has O_DIRECT implemented) for it work.
If it works at all, it works the way you use.
> 2. Which "open" is called. Can someone give me a
> pointer to the source file where this is implemented.
> I am guessing this "open" is like a generic one, as
> opposed to the ones implemented in ext2, ext3,
> jfs...etc directories.
When the inode is looked up and the fs driver finds it's a special
inode, it calls a special setup routine to set apropriate operations
vector. IIRC it's called make_special_inode.
> 3. I am getting an error when I try to issue a lseek
> on the opened device:
>
> lseek (fd, 200, SEEK_SET);
>
> I am getting "Invalid Argument", am I not allowed to
> use SEEK_SET, if so why?
>
> 4. Again, any pointer to the source file where this
> "lseek" is implemented.
Almost all syscall entry points are called sys_<name> and so is lseek.
The real entry point is thus called sys_lseek. The specific
implementation is file operations llseek, you can look it up in the
file_operations struct that make_special_inode sets for relevant (block)
devices.
-------------------------------------------------------------------------------
Jan 'Bulb' Hudec <bulb@ucw.cz>
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