From mboxrd@z Thu Jan  1 00:00:00 1970
From: kai@gnukai.com (Kai Meyer)
Date: Mon, 14 Nov 2011 12:15:14 -0700
Subject: Generic I/O
Message-ID: <4EC168C2.8090402@gnukai.com>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

I'm finding it's really simple to write generic I/O functions for block 
devices (via a "struct block_device") to mimic the posix read() and 
write() functions (I have to supply the position, since I don't have a 
fd to keep a position for me, but that's perfectly ok).

I've got a little hack that allows me to run synchronously or 
asynchronously, relying on submit_bio() to create the threads for me. My 
caller function has an atomic_t value that I set equal to the number of 
bios I want to submit. Then I pass a pointer to that atomic_t around to 
each of the bios which decrement it in the endio function for that bio.

Then the caller does this:
while(atomic_read(numbios) > 0)
         msleep(1);

I'm finding the msleep(1) is a really really really long time, 
relatively. It seems to work ok if I just have an empty loop, but it 
also seems to me like I'm re-inventing a wheel here. Are there 
mechanisms that are better suited for waiting for tasks to complete? Or 
even for generic block I/O functions?

-Kai Meyer