On 09/05/2016 18:21, Warner Losh wrote:
On May 9, 2016, at 11:14 AM, Steven Hartland <ste...@multiplay.co.uk> wrote:On 09/05/2016 18:04, Alan Somers wrote:On Wed, Feb 17, 2016 at 10:16 AM, Warner Losh <i...@freebsd.org> wrote: Author: imp Date: Wed Feb 17 17:16:02 2016 New Revision: 295707 URL: https://svnweb.freebsd.org/changeset/base/295707 Log: Create an API to reset a struct bio (g_reset_bio). This is mandatory for all struct bio you get back from g_{new,alloc}_bio. Temporary bios that you create on the stack or elsewhere should use this before first use of the bio, and between uses of the bio. At the moment, it is nothing more than a wrapper around bzero, but that may change in the future. The wrapper also removes one place where we encode the size of struct bio in the KBI. Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c head/sys/dev/mmc/mmcsd.c head/sys/dev/virtio/block/virtio_blk.c head/sys/geom/geom.h head/sys/geom/geom_io.c head/sys/geom/journal/g_journal.c head/sys/geom/mirror/g_mirror.c head/sys/geom/raid/g_raid.c head/sys/geom/raid3/g_raid3.c head/sys/kern/kern_physio.c smh noticed that while your commit message says that g_reset_bio is mandatory after g_{new,alloc}_bio, your diff only replaced existing calls to bzero. You didn't insert g_reset_bio calls after all g_alloc_bio calls, for example in vdev_geom_io_start. Do you intend to follow up this change with a g_reset_bio everywhere that g_alloc_bio is called, or did you mean that g_reset_bio is optional after all bios returned by g_{new,alloc}_bio?Yer I was just penning this too: This commit was just referenced in https://reviews.freebsd.org/D6153 It seems rather odd to require all callers to g_{new,alloc}_bio to also call g_reset_bio.I don’t. Please see my other reply. It’s only when you *RE*use the bio that you need to call g_reset_bio(), not when you use it in the first place. You can no longer call bzero() on the bio to reset it.I assume this is because uma can return an existing object instead of fresh one hence its not guaranteed to be bzeroed? If so why have the caller responsible, seems petty error prone. A quick look at users of g_alloc_bio it seems like this is something that's not done currently done in all places, even some usages of memset still hanging around, are these cases a bug?No. That’s not the case at all. There’s going to be contents of the BIO that cannot be blithely cleared by the users of the memory. Many other structures in the kernel are like this, but bio wasn’t previously.If the concept of this was to ensure correctly initialised objects from uma would the callback handers to uma_zcreate not be a better option as that would guarantee things are correct instead of leaving it to the caller?No. It’s to ensure internal state to the bio isn’t blown away by a subsequent bzero() call before calling g_destroy_bio().As a side matter, this area really needs some man pages so the its clear to all what is needed and when.Agreed. The whole storage stack, however, is wonderfully under-documented. I’ve started documenting CAM, but handn’t worked my way back to geom…
Thanks for the clarifications Warner, appreciated :)
Regards
Steve
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