[PATCH 5/6] xfs: add log attributes for log lsn and grant head data

[Brian Foster]

On Thu, Jun 26, 2014 at 02:52:56PM +1000, Dave Chinner wrote:
> On Fri, Jun 06, 2014 at 09:13:33AM -0400, Brian Foster wrote:
> > Create log attributes to export the current runtime state of the log to
> > sysfs. Note that the filesystem should be frozen for consistency across
> > attributes.
> > 
> > The following per-mount attributes are created: log_head_lsn,
> > log_tail_lsn, reserve_grant_head and write_grant_head. These represent
> > the physical log head, tail and reserve and write grant heads
> > respectively. Attribute values are exported in the following format:
> > 
> > 	"cycle:[block,byte]"
> > 
> > ... where cycle represents the log cycle and [block,bytes] represents
> > either the basic block or byte offset of the log, depending on the
> > attribute.  Log sequence number (LSN) values are encoded in basic blocks
> > and grant heads are encoded in bytes. All values are in decimal format.
> > 
> > Signed-off-by: Brian Foster <bfoster at redhat.com>
> > ---
> >  fs/xfs/xfs_sysfs.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 66 insertions(+)
> > 
> > diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
> > index f837527..fbd82d5 100644
> > --- a/fs/xfs/xfs_sysfs.c
> > +++ b/fs/xfs/xfs_sysfs.c
> > @@ -23,6 +23,9 @@
> >  #include "xfs_trans_resv.h"
> >  #include "xfs_ag.h"
> >  #include "xfs_mount.h"
> > +#include "xfs_log_format.h"
> > +#include "xfs_log.h"
> > +#include "xfs_log_priv.h"
> >  
> >  struct xfs_sysfs_attr {
> >  	struct attribute attr;
> > @@ -57,7 +60,70 @@ struct kobj_type xfs_mp_ktype = {
> >  
> >  /* xlog */
> >  
> > +STATIC ssize_t
> > +log_head_lsn_show(
> > +	char	*buf,
> > +	void	*data)
> > +{
> > +	struct xlog *log = data;
> > +	int ret;
> > +
> > +	spin_lock(&log->l_icloglock);
> > +	ret = snprintf(buf, PAGE_SIZE, "%d:%d\n", log->l_curr_cycle,
> > +			log->l_curr_block);
> > +	spin_unlock(&log->l_icloglock);
> 
> I'd keep the snprintf() outside the iclog lock, just so sampling
> perturbs behaviour as little as possible. i.e. use cycle/block
> locals as per all the others.
> 

Ok, will fix...

> Otherwise, looks good.
> 
> Reviewed-by: Dave Chinner <dchinner at redhat.com>
> 

Thanks!

Brian

> -- 
> Dave Chinner
> david at fromorbit.com