Messages in this thread | | | Date | Thu, 10 Jan 2008 15:43:25 -0500 | From | Pete Wyckoff <> | Subject | Re: [PATCH] bsg : Add support for io vectors in bsg |
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fujita.tomonori@lab.ntt.co.jp wrote on Wed, 09 Jan 2008 09:11 +0900: > On Tue, 8 Jan 2008 17:09:18 -0500 > Pete Wyckoff <pw@osc.edu> wrote: > > I took another look at the compat approach, to see if it is feasible > > to keep the compat handling somewhere else, without the use of #ifdef > > CONFIG_COMPAT and size-comparison code inside bsg.c. I don't see how. > > The use of iovec is within a write operation on a char device. It's > > not amenable to a compat_sys_ or a .compat_ioctl approach. > > > > I'm partial to #1 because the use of architecture-independent fields > > matches the rest of struct sg_io_v4. But if you don't want to have > > another iovec type in the kernel, could we do #2 but just return > > -EINVAL if the need for compat is detected? I.e. change > > dout_iovec_count to dout_iovec_length and do the math? > > If you are ok with removing the write/read interface and just have > ioctl, we could can handle comapt stuff like others do. But I think > that you (OSD people) really want to keep the write/read > interface. Sorry, I think that there is no workaround to support iovec > in bsg.
I don't care about read/write in particular. But we do need some way to launch asynchronous SCSI commands, and currently read/write are the only way to do that in bsg. The reason is to keep multiple spindles busy at the same time.
How about these new ioctls instead of read/write:
SG_IO_SUBMIT - start a new blk_execute_rq_nowait() SG_IO_TEST - complete and return a previous req SG_IO_WAIT - wait for a req to finish, interruptibly
Then old write users will instead do ioctl SUBMIT. Read users will do TEST for non-blocking fd, or WAIT for blocking. And SG_IO could be implemented as SUBMIT + WAIT.
Then we can do compat_ioctl and convert up iovecs out-of-line before calling the normal functions.
Let me know if you want a patch for this.
-- Pete
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