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SubjectRe: How to setup a buffer_head in a driver
On Tuesday 14 January 2003 02:35 pm, Brian Kelly wrote:
> Hi,
> I'm writing a device driver that among other things needs to write data,
> manufactured by the driver itself, to a block device.
> I have this data in block sized kmalloc()'d chunks. So what I'm doing is
> allocating a struct buffer_head, initialising it, fill out it's various
> fields and send it to generic_make_request().

It's probably better to use submit_bh(). Set the BH_Lock and BH_Mapped bits,
also set up b_end_io. Then do a wait_on_buffer(), wait for the IO to
complete. There's some similar code in

However, what you're doing is an odd thing. If there is already pagecache
against that block device then the kernel doesn't know that you've changed
the bytes on-disk and will cheerfully proceed to use (and write out) the
cached data. You'll lose your modifications..

It would be better to use sb_getblk() or bread(), to lock the returned
buffer_head, then copy your data into it and to then write it back with
submit_bh() or ll_rw_block(). Or just leave it dirty and let the kernel
write it out in due course.

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