how to bypass buffer cache for a block device driver

T. P. Saravanan (sara@procsys.com)
Sat, 07 Aug 1999 18:06:35 +0530

I've a custom hardware with lot of inbuilt cache.
I want to write a block device driver for it and i
*want to bypass the buffer cache*.
I intend to run filesystems on top of it.

I filled in the "read" and "write" functions with my own versions
and bypassed "block_read" and "block_write".
I could "fdisk" but mount failed complaining about "request_fn".

I filled in the "request_fn" and now, it appears to me
that all io happens through "request_fn". For instance,
"printk" lines in "read" and "write" print
nothing.

If i check the pid in "request_fn" it is that
of "kflushd" or "bdflush".

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Is it possible to bypass the buffer cache completely 
for a block device driver? What should I do?


Is it possible to bypass only for some processes and 
let thro for others? (This is the final behaviour I want.)


Where should I look for more about block device 
drivers and their interaction with buffer cache (i.e. apart from 
code in terms of design, structure etc.,).



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I am not on the mailing list, so please post a copy to 
"sara@procsys.com" too.



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Thanks in advance


Saravanan


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