Re: [PATCH RFC v0 10/49] pnfsd: use sbid hash table to map super_blocks to devid major identifiers

["J. Bruce Fields" <bfields@redhat.com>]

On Wed, Oct 02, 2013 at 05:32:32PM +0300, Benny Halevy wrote:
> On 2013-10-02 01:14, J. Bruce Fields wrote:
> > See previous comments.  What guarantees these superblock pointers stay
> > good as long as they're in the cache?
> 
> Currently, the dependency on nfsd.ko should hold them but that should go away.

I don't see how that prevents anyone from unmounting a filesystem.

> Trying to think about referencing svc_export instead, we use find_sbid_id
> to get to the superblock in nfsd4_getdevinfo since we have no current fh.
> And we need the superblock to call into the fs sb->s_pnfs_op->get_device_info
> later in nfsd4_encode_getdevinfo.
> 
> Just to make sure, we can safely get to the sb via exp->ex_path.dentry->d_inode->i_sb
> right?

Right.

--b.

> 
> Benny
> 
> > 
> > --b.
> > 
> > On Thu, Sep 26, 2013 at 02:40:31PM -0400, Benny Halevy wrote:
> >> From: Benny Halevy <bhalevy@panasas.com>
> >>
> >> Signed-off-by: Benny Halevy <bhalevy@panasas.com>
> >> [pnfsd: alloc_sid should kmalloc a object not a pointer]
> >> Signed-off-by: Bian Naimeng <biannm@cn.fujitsu.com>
> >> Signed-off-by: Benny Halevy <bhalevy@panasas.com>
> >> Signed-off-by: Benny Halevy <bhalevy@primarydata.com>
> >> ---
> >>  fs/nfsd/nfs4pnfsd.c | 120 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  fs/nfsd/pnfsd.h     |   2 +
> >>  2 files changed, 122 insertions(+)
> >>
> >> diff --git a/fs/nfsd/nfs4pnfsd.c b/fs/nfsd/nfs4pnfsd.c
> >> index cb28207..9a7cbc9 100644
> >> --- a/fs/nfsd/nfs4pnfsd.c
> >> +++ b/fs/nfsd/nfs4pnfsd.c
> >> @@ -25,3 +25,123 @@
> >>  
> >>  #define NFSDDBG_FACILITY                NFSDDBG_PNFS
> >>  
> >> +static DEFINE_SPINLOCK(layout_lock);
> >> +
> >> +/* hash table for nfsd4_pnfs_deviceid.sbid */
> >> +#define SBID_HASH_BITS	8
> >> +#define SBID_HASH_SIZE	(1 << SBID_HASH_BITS)
> >> +#define SBID_HASH_MASK	(SBID_HASH_SIZE - 1)
> >> +
> >> +struct sbid_tracker {
> >> +	u64 id;
> >> +	struct super_block *sb;
> >> +	struct list_head hash;
> >> +};
> >> +
> >> +static u64 current_sbid;
> >> +static struct list_head sbid_hashtbl[SBID_HASH_SIZE];
> >> +
> >> +static unsigned long
> >> +sbid_hashval(struct super_block *sb)
> >> +{
> >> +	return hash_ptr(sb, SBID_HASH_BITS);
> >> +}
> >> +
> >> +static struct sbid_tracker *
> >> +alloc_sbid(void)
> >> +{
> >> +	return kmalloc(sizeof(struct sbid_tracker), GFP_KERNEL);
> >> +}
> >> +
> >> +static void
> >> +destroy_sbid(struct sbid_tracker *sbid)
> >> +{
> >> +	spin_lock(&layout_lock);
> >> +	list_del(&sbid->hash);
> >> +	spin_unlock(&layout_lock);
> >> +	kfree(sbid);
> >> +}
> >> +
> >> +void
> >> +nfsd4_free_pnfs_slabs(void)
> >> +{
> >> +	int i;
> >> +	struct sbid_tracker *sbid;
> >> +
> >> +	for (i = 0; i < SBID_HASH_SIZE; i++) {
> >> +		while (!list_empty(&sbid_hashtbl[i])) {
> >> +			sbid = list_first_entry(&sbid_hashtbl[i],
> >> +						struct sbid_tracker,
> >> +						hash);
> >> +			destroy_sbid(sbid);
> >> +		}
> >> +	}
> >> +}
> >> +
> >> +int
> >> +nfsd4_init_pnfs_slabs(void)
> >> +{
> >> +	int i;
> >> +
> >> +	for (i = 0; i < SBID_HASH_SIZE; i++)
> >> +		INIT_LIST_HEAD(&sbid_hashtbl[i]);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +static u64
> >> +alloc_init_sbid(struct super_block *sb)
> >> +{
> >> +	struct sbid_tracker *sbid;
> >> +	struct sbid_tracker *new = alloc_sbid();
> >> +	unsigned long hash_idx = sbid_hashval(sb);
> >> +	u64 id = 0;
> >> +
> >> +	if (likely(new)) {
> >> +		spin_lock(&layout_lock);
> >> +		id = ++current_sbid;
> >> +		new->id = (id << SBID_HASH_BITS) | (hash_idx & SBID_HASH_MASK);
> >> +		id = new->id;
> >> +		BUG_ON(id == 0);
> >> +		new->sb = sb;
> >> +
> >> +		list_for_each_entry (sbid, &sbid_hashtbl[hash_idx], hash)
> >> +			if (sbid->sb == sb) {
> >> +				kfree(new);
> >> +				id = sbid->id;
> >> +				spin_unlock(&layout_lock);
> >> +				return id;
> >> +			}
> >> +		list_add(&new->hash, &sbid_hashtbl[hash_idx]);
> >> +		spin_unlock(&layout_lock);
> >> +	}
> >> +	return id;
> >> +}
> >> +
> >> +static u64
> >> +find_create_sbid(struct super_block *sb)
> >> +{
> >> +	struct sbid_tracker *sbid;
> >> +	unsigned long hash_idx = sbid_hashval(sb);
> >> +	int pos = 0;
> >> +	u64 id = 0;
> >> +
> >> +	spin_lock(&layout_lock);
> >> +	list_for_each_entry (sbid, &sbid_hashtbl[hash_idx], hash) {
> >> +		pos++;
> >> +		if (sbid->sb != sb)
> >> +			continue;
> >> +		if (pos > 1) {
> >> +			list_del(&sbid->hash);
> >> +			list_add(&sbid->hash, &sbid_hashtbl[hash_idx]);
> >> +		}
> >> +		id = sbid->id;
> >> +		break;
> >> +	}
> >> +	spin_unlock(&layout_lock);
> >> +
> >> +	if (!id)
> >> +		id = alloc_init_sbid(sb);
> >> +
> >> +	return id;
> >> +}
> >> diff --git a/fs/nfsd/pnfsd.h b/fs/nfsd/pnfsd.h
> >> index 7c46791..29ea2e7 100644
> >> --- a/fs/nfsd/pnfsd.h
> >> +++ b/fs/nfsd/pnfsd.h
> >> @@ -36,4 +36,6 @@
> >>  
> >>  #include <linux/nfsd/nfsd4_pnfs.h>
> >>  
> >> +#include "xdr4.h"
> >> +
> >>  #endif /* LINUX_NFSD_PNFSD_H */
> >> -- 
> >> 1.8.3.1
> >>
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >