Re: [PATCH 7/9] xfs: Add attr context to log item

[Brian Foster <bfoster@redhat.com>]

On Mon, Apr 22, 2019 at 03:01:27PM -0700, Allison Henderson wrote:
> 
> 
> On 4/22/19 6:03 AM, Brian Foster wrote:
> > On Fri, Apr 12, 2019 at 03:50:34PM -0700, Allison Henderson wrote:
> > > This patch modifies xfs_attr_item to store a xfs_da_args, a xfs_buf pointer
> > > and a new state type. We will use these in the next patch when
> > > we modify xfs_set_attr_args to roll transactions by returning EAGAIN.
> > > Because the subroutines of this function modify the contents of these
> > > structures, we need to find a place to store them where they remain
> > > instantiated across multiple calls to xfs_set_attr_args.
> > > 
> > > Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> > > ---
> > 
> > I see Darrick has already commented on the whole state thing. I'll
> > probably have to grok the next patch to comment further, but just a
> > couple initial thoughts:
> > 
> > First, I hit a build failure with this patch. It looks like there's a
> > missed include in the scrub code:
> > 
> >    ...
> >    CC [M]  fs/xfs/scrub/repair.o
> > In file included from fs/xfs/scrub/repair.c:32:
> > fs/xfs/libxfs/xfs_attr.h:105:21: error: field ‘xattri_args’ has incomplete type
> >    struct xfs_da_args xattri_args;   /* args context */
> Hmm, ok.  I'll get that corrected, I probably need to clean out my workspace
> and build from scratch.
> 
> >    ...
> > 
> > Second, the commit log suggests that the states will reflect the current
> > transaction roll points (i.e., establishing re-entry points down in
> > xfs_attr_set_args(). I'm kind of wondering if we should break these
> > xattr set sub-sequences down into smaller helper functions (refactoring
> > the existing code as we go) such that the mechanism could technically be
> > used deferred or not. Re: the previous thought on whether to defer xattr
> > removes or not, there might also be cases where there's not a need to
> > defer xattr sets.
> > 
> > E.g., taking a quick peek into the next patch, the state 1 case in
> > xfs_attr_try_sf_addname() is actually a transaction commit, which I
> > think means we're done. We'd have done an attr memory allocation,
> > deferred op and transaction roll where none was necessary so it might
> > not be worth it to defer in that scenario. Hmm, it also looks like we
> > return -EAGAIN in places where we've not actually done any work, like if
> > a shortform add attempt returns -ENOSPC (or the -EAGAIN return before we
> > even attempt the sf add). That kind of looks like a waste of transaction
> > rolls and further suggests it might be cleaner to break this whole path
> > down into helpers and put it back together in a way more conducive to
> > deferred operations.
> 
> Yes, this area is a bit of a wart the way it is right now.  I think you're
> right in that ultimately we may end up having to do a lot of refactoring in
> order to have more efficient "re-entry points".  The state machine is hard
> to get into subroutines, so it's limited in use in the top level function.
> 
> I was also starting to wonder if maybe I could do some refactoring in
> xfs_defer_finish_noroll to capture the common code associated with the
> -EAGAIN handling.  Then maybe we could make a function pointer that we can
> pass through the finish_item interface.  The idea being that subroutines
> could use the function pointer to cycle out the transaction when needed
> instead of having to record states and back out like this. It'd be a new
> parameter to pipe around, but it'd be more efficient than the state machine,
> and less surgery in the refactor.  And maybe a blessing to any other
> operations that might need to go through this transition in the future.
> Thoughts?
> 

That's an interesting idea. It still strikes me as a bit of a
fallback/hack as opposed to organizing the code to properly fit into the
dfops infrastructure, but it could be useful as a transient solution.
>From a high level, it looks like we'd have to create a new intent, relog
this item and all remaining items associated with the dfp to it, roll
the tx, and finally create a done item associated with the intent in the
new tx. You'd need access to the dfp for some of that, so it's not
immediately clear to me that this ends up much easier than fixing up
the xattr code.

BTW, if we did end up with something like that I'd probably prefer to
see it as an exported dfops helper function as opposed to a function
pointer being passed around, if possible.

Brian

> Thanks again for the reviews!
> 
> Allison
> 
> > 
> > Brian
> > 
> > 
> > >   fs/xfs/libxfs/xfs_attr.h | 18 +++++++++++++++++-
> > >   fs/xfs/scrub/common.c    |  2 ++
> > >   fs/xfs/xfs_acl.c         |  2 ++
> > >   fs/xfs/xfs_attr_item.c   |  2 +-
> > >   fs/xfs/xfs_ioctl.c       |  2 ++
> > >   fs/xfs/xfs_ioctl32.c     |  2 ++
> > >   fs/xfs/xfs_iops.c        |  1 +
> > >   fs/xfs/xfs_xattr.c       |  1 +
> > >   8 files changed, 28 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> > > index 974c963..4ce3b0a 100644
> > > --- a/fs/xfs/libxfs/xfs_attr.h
> > > +++ b/fs/xfs/libxfs/xfs_attr.h
> > > @@ -77,6 +77,13 @@ typedef struct attrlist_ent {	/* data from attr_list() */
> > >   	char	a_name[1];	/* attr name (NULL terminated) */
> > >   } attrlist_ent_t;
> > > +/* Attr state machine types */
> > > +enum xfs_attr_state {
> > > +	XFS_ATTR_STATE1 = 1,
> > > +	XFS_ATTR_STATE2 = 2,
> > > +	XFS_ATTR_STATE3 = 3,
> > > +};
> > > +
> > >   /*
> > >    * List of attrs to commit later.
> > >    */
> > > @@ -88,7 +95,16 @@ struct xfs_attr_item {
> > >   	void		  *xattri_name;	      /* attr name */
> > >   	uint32_t	  xattri_name_len;    /* length of name */
> > >   	uint32_t	  xattri_flags;       /* attr flags */
> > > -	struct list_head  xattri_list;
> > > +
> > > +	/*
> > > +	 * Delayed attr parameters that need to remain instantiated
> > > +	 * across transaction rolls during the defer finish
> > > +	 */
> > > +	struct xfs_buf		*xattri_leaf_bp;  /* Leaf buf to release */
> > > +	enum xfs_attr_state	xattri_state;	  /* state machine marker */
> > > +	struct xfs_da_args	xattri_args;	  /* args context */
> > > +
> > > +	struct list_head	xattri_list;
> > >   	/*
> > >   	 * A byte array follows the header containing the file name and
> > > diff --git a/fs/xfs/scrub/common.c b/fs/xfs/scrub/common.c
> > > index 0c54ff5..270c32e 100644
> > > --- a/fs/xfs/scrub/common.c
> > > +++ b/fs/xfs/scrub/common.c
> > > @@ -30,6 +30,8 @@
> > >   #include "xfs_rmap_btree.h"
> > >   #include "xfs_log.h"
> > >   #include "xfs_trans_priv.h"
> > > +#include "xfs_da_format.h"
> > > +#include "xfs_da_btree.h"
> > >   #include "xfs_attr.h"
> > >   #include "xfs_reflink.h"
> > >   #include "scrub/xfs_scrub.h"
> > > diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c
> > > index 142de8d..9b1b93e 100644
> > > --- a/fs/xfs/xfs_acl.c
> > > +++ b/fs/xfs/xfs_acl.c
> > > @@ -10,6 +10,8 @@
> > >   #include "xfs_mount.h"
> > >   #include "xfs_inode.h"
> > >   #include "xfs_acl.h"
> > > +#include "xfs_da_format.h"
> > > +#include "xfs_da_btree.h"
> > >   #include "xfs_attr.h"
> > >   #include "xfs_trace.h"
> > >   #include <linux/slab.h>
> > > diff --git a/fs/xfs/xfs_attr_item.c b/fs/xfs/xfs_attr_item.c
> > > index 0ea19b4..36e6d1e 100644
> > > --- a/fs/xfs/xfs_attr_item.c
> > > +++ b/fs/xfs/xfs_attr_item.c
> > > @@ -19,10 +19,10 @@
> > >   #include "xfs_rmap.h"
> > >   #include "xfs_inode.h"
> > >   #include "xfs_icache.h"
> > > -#include "xfs_attr.h"
> > >   #include "xfs_shared.h"
> > >   #include "xfs_da_format.h"
> > >   #include "xfs_da_btree.h"
> > > +#include "xfs_attr.h"
> > >   static inline struct xfs_attri_log_item *ATTRI_ITEM(struct xfs_log_item *lip)
> > >   {
> > > diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> > > index ab341d6..c8728ca 100644
> > > --- a/fs/xfs/xfs_ioctl.c
> > > +++ b/fs/xfs/xfs_ioctl.c
> > > @@ -16,6 +16,8 @@
> > >   #include "xfs_rtalloc.h"
> > >   #include "xfs_itable.h"
> > >   #include "xfs_error.h"
> > > +#include "xfs_da_format.h"
> > > +#include "xfs_da_btree.h"
> > >   #include "xfs_attr.h"
> > >   #include "xfs_bmap.h"
> > >   #include "xfs_bmap_util.h"
> > > diff --git a/fs/xfs/xfs_ioctl32.c b/fs/xfs/xfs_ioctl32.c
> > > index 5001dca..23f6990 100644
> > > --- a/fs/xfs/xfs_ioctl32.c
> > > +++ b/fs/xfs/xfs_ioctl32.c
> > > @@ -21,6 +21,8 @@
> > >   #include "xfs_fsops.h"
> > >   #include "xfs_alloc.h"
> > >   #include "xfs_rtalloc.h"
> > > +#include "xfs_da_format.h"
> > > +#include "xfs_da_btree.h"
> > >   #include "xfs_attr.h"
> > >   #include "xfs_ioctl.h"
> > >   #include "xfs_ioctl32.h"
> > > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> > > index e73c21a..561c467 100644
> > > --- a/fs/xfs/xfs_iops.c
> > > +++ b/fs/xfs/xfs_iops.c
> > > @@ -17,6 +17,7 @@
> > >   #include "xfs_acl.h"
> > >   #include "xfs_quota.h"
> > >   #include "xfs_error.h"
> > > +#include "xfs_da_btree.h"
> > >   #include "xfs_attr.h"
> > >   #include "xfs_trans.h"
> > >   #include "xfs_trace.h"
> > > diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c
> > > index 3013746..938e81d 100644
> > > --- a/fs/xfs/xfs_xattr.c
> > > +++ b/fs/xfs/xfs_xattr.c
> > > @@ -11,6 +11,7 @@
> > >   #include "xfs_mount.h"
> > >   #include "xfs_da_format.h"
> > >   #include "xfs_inode.h"
> > > +#include "xfs_da_btree.h"
> > >   #include "xfs_attr.h"
> > >   #include "xfs_attr_leaf.h"
> > >   #include "xfs_acl.h"
> > > -- 
> > > 2.7.4
> > >