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

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH 5/6] xfs: add log attributes for log lsn and grant head data
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 26 Jun 2014 14:52:56 +1000
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1402060414-22075-6-git-send-email-bfoster@xxxxxxxxxx>
References: <1402060414-22075-1-git-send-email-bfoster@xxxxxxxxxx> <1402060414-22075-6-git-send-email-bfoster@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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@xxxxxxxxxx>
> ---
>  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.

Otherwise, looks good.

Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>

-- 
Dave Chinner
david@xxxxxxxxxxxxx

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