[Devel] Re: [patch 1/5][RFC - ipv4/udp checkpoint/restart] : add lookup for unhashed inode

[Serge E. Hallyn]

Quoting dlezcano at fr.ibm.com (dlezcano at fr.ibm.com):
> The socket relies on the sockfs. In some cases, the socket are orphans and
> it is not possible to access them via a file descriptor, this is the case for
> example for timewait sockets. Hopefully, an inode is still usable to specify
> a socket. This one can be retrieved from /proc/net/tcp for orphan sockets or
> from a fstat.
> 
> When a socket is created the socket inode is added to the sockfs.
> Unfortunatly, this one is not stored into the hashed inode list, so
> I need a helper to browse the inode list contained in the superblock 
> of the sockfs.
> 
> This is one solution, another solution is to stored the inode into
> the hashed list when socket is created.

I assume that would be unacceptable overhead on a very busy server.
Walking all the inodes NUM_INODES(task_set) for a checkpoint could
be a real bottleneck, but at least it's only at checkpoint time.

Have you checked net-dev archives for discussions about not hashing
these inodes?  I suppose at some point you'll want to ask there what the
preference is.

But certainly for now this seems the right approach.

> Signed-off-by: Daniel Lezcano <dlezcano at fr.ibm.com>
Acked-by: Serge E. Hallyn <serue at us.ibm.com>

(Or whatever tag they decide over on lkml that I should be using  :)

thanks,
-serge

PS - I won't be acking other patches bc I just haven't looked at
netlink enough - so don't read anything more into that :)

> ---
>  fs/inode.c         |   29 +++++++++++++++++++++++++++++
>  include/linux/fs.h |    1 +
>  2 files changed, 30 insertions(+)
> 
> Index: 2.6.20-cr/fs/inode.c
> ===================================================================
> --- 2.6.20-cr.orig/fs/inode.c
> +++ 2.6.20-cr/fs/inode.c
> @@ -877,6 +877,35 @@
> 
>  EXPORT_SYMBOL(ilookup);
> 
> +
> +/**
> + * ilookup_unhased - search for an inode in the superblock
> + * @sb:		super block of file system to search
> + * @ino:	inode number to search for
> + *
> + * The ilookup_unhashed browse the superblock inode list to find the inode.
> + *
> + * If the inode is found in the inode list stored in the superblock, the inode is
> + * with an incremented reference count.
> + *
> + * Otherwise NULL is returned.
> + */
> +struct inode *ilookup_unhashed(struct super_block *sb, unsigned long ino)
> +{
> +	struct inode *inode = NULL;
> +
> +	spin_lock(&inode_lock);
> +	list_for_each_entry(inode, &sb->s_inodes, i_sb_list)
> +		if (inode->i_ino == ino) {
> +			__iget(inode);
> +			break;
> +		}
> +	spin_unlock(&inode_lock);
> +	return inode;
> +
> +}
> +EXPORT_SYMBOL(ilookup_unhashed);
> +
>  /**
>   * iget5_locked - obtain an inode from a mounted file system
>   * @sb:		super block of file system
> Index: 2.6.20-cr/include/linux/fs.h
> ===================================================================
> --- 2.6.20-cr.orig/include/linux/fs.h
> +++ 2.6.20-cr/include/linux/fs.h
> @@ -1657,6 +1657,7 @@
>  extern struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
>  		int (*test)(struct inode *, void *), void *data);
>  extern struct inode *ilookup(struct super_block *sb, unsigned long ino);
> +extern struct inode *ilookup_unhashed(struct super_block *sb, unsigned long ino);
> 
>  extern struct inode * iget5_locked(struct super_block *, unsigned long, int (*test)(struct inode *, void *), int (*set)(struct inode *, void *), void *);
>  extern struct inode * iget_locked(struct super_block *, unsigned long);
> 
> -- 
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