So, I'm working on a block driver using the make_request_fn
interface, and have to handle a bio that comes in with
(bi_rw & REQ_FLUSH) set AND data to transfer.
According to Documentation/block/writeback_cache_control.txt:
The REQ_FLUSH flag can be OR ed into the r/w flags of a
bio submitted from the filesystem and will make sure the
volatile cache of the storage device has been flushed
before the actual I/O operation is started.
So I've written code that handles that case, along with the
various error cases I might encounter, I think, which leads
to my question:
How do I get such a bio with a data transfer AND the REQ_FLUSH bit
set to come into the driver? Just wondering how to test this case.
Thanks,
(I cc'ed Tejun Heo just because his name is in block/blk-flush.c)
-- steve
On Fri, Aug 09, 2013 at 02:09:34PM -0500, [email protected] wrote:
>
> So, I'm working on a block driver using the make_request_fn
> interface, and have to handle a bio that comes in with
> (bi_rw & REQ_FLUSH) set AND data to transfer.
>
> According to Documentation/block/writeback_cache_control.txt:
>
> The REQ_FLUSH flag can be OR ed into the r/w flags of a
> bio submitted from the filesystem and will make sure the
> volatile cache of the storage device has been flushed
> before the actual I/O operation is started.
>
> So I've written code that handles that case, along with the
> various error cases I might encounter, I think, which leads
> to my question:
>
> How do I get such a bio with a data transfer AND the REQ_FLUSH bit
> set to come into the driver? Just wondering how to test this case.
>
> Thanks,
>
> (I cc'ed Tejun Heo just because his name is in block/blk-flush.c)
>
> -- steve
Oops, you'd think I'd know Jens's email address by now.
-- steve
Hi,
On Fri, 2013-08-09 at 14:09 -0500, [email protected] wrote:
> So, I'm working on a block driver using the make_request_fn
> interface, and have to handle a bio that comes in with
> (bi_rw & REQ_FLUSH) set AND data to transfer.
>
> According to Documentation/block/writeback_cache_control.txt:
>
> The REQ_FLUSH flag can be OR ed into the r/w flags of a
> bio submitted from the filesystem and will make sure the
> volatile cache of the storage device has been flushed
> before the actual I/O operation is started.
>
> So I've written code that handles that case, along with the
> various error cases I might encounter, I think, which leads
> to my question:
>
> How do I get such a bio with a data transfer AND the REQ_FLUSH bit
> set to come into the driver? Just wondering how to test this case.
>
GFS2 does this... if you look at the log flush code and the function
log_write_header() in particular, you'll see that it sets this on each
log header that gets written. You don't need a cluster to generate this
kind of i/o, just supply mkfs.gfs2 with -p lock_nolock and mount it as a
local filesystem. The combination of touch foo; sync should be enough to
generate a log flush writing a log header with this flag set,
Steve.
> Thanks,
>
> (I cc'ed Tejun Heo just because his name is in block/blk-flush.c)
>
> -- steve
>
> --
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On Fri, Aug 09, 2013 at 09:18:15PM +0100, Steven Whitehouse wrote:
> Hi,
>
> On Fri, 2013-08-09 at 14:09 -0500, [email protected] wrote:
> > So, I'm working on a block driver using the make_request_fn
> > interface, and have to handle a bio that comes in with
> > (bi_rw & REQ_FLUSH) set AND data to transfer.
> >
> > According to Documentation/block/writeback_cache_control.txt:
> >
> > The REQ_FLUSH flag can be OR ed into the r/w flags of a
> > bio submitted from the filesystem and will make sure the
> > volatile cache of the storage device has been flushed
> > before the actual I/O operation is started.
> >
> > So I've written code that handles that case, along with the
> > various error cases I might encounter, I think, which leads
> > to my question:
> >
> > How do I get such a bio with a data transfer AND the REQ_FLUSH bit
> > set to come into the driver? Just wondering how to test this case.
> >
> GFS2 does this... if you look at the log flush code and the function
> log_write_header() in particular, you'll see that it sets this on each
> log header that gets written. You don't need a cluster to generate this
> kind of i/o, just supply mkfs.gfs2 with -p lock_nolock and mount it as a
> local filesystem. The combination of touch foo; sync should be enough to
> generate a log flush writing a log header with this flag set,
Thanks!
Turns out ext3 seems to do it as well (now I feel kind of dumb
for asking -- had tried with ext2, and had tried some writes
with a file descriptor with O_SYNC set, but I was kind of shooting
in the dark.)
And my code appears to work too.
-- steve