Merge git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6

* git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6:
[NFS] Set CONFIG_KEYS when CONFIG_NFS_USE_KERNEL_DNS is set
AFS: Implement an autocell mount capability [ver #2]
DNS: If the DNS server returns an error, allow that to be cached [ver #2]
NFS: Use kernel DNS resolver [ver #2]
cifs: update README to include details about 'fsc' option

fs/afs/cell.c

···
  * allocate a cell record and fill in its name, VL server address list and
  * allocate an anonymous key
  */
-static struct afs_cell *afs_cell_alloc(const char *name, char *vllist)
+static struct afs_cell *afs_cell_alloc(const char *name, unsigned namelen,
+				       char *vllist)
 {
 	struct afs_cell *cell;
 	struct key *key;
-	size_t namelen;
 	char keyname[4 + AFS_MAXCELLNAME + 1], *cp, *dp, *next;
 	char  *dvllist = NULL, *_vllist = NULL;
 	char  delimiter = ':';
 	int ret;
 
-	_enter("%s,%s", name, vllist);
+	_enter("%*.*s,%s", namelen, namelen, name ?: "", vllist);
 
 	BUG_ON(!name); /* TODO: want to look up "this cell" in the cache */
 
-	namelen = strlen(name);
 	if (namelen > AFS_MAXCELLNAME) {
 		_leave(" = -ENAMETOOLONG");
 		return ERR_PTR(-ENAMETOOLONG);
···
 	if (!vllist || strlen(vllist) < 7) {
 		ret = dns_query("afsdb", name, namelen, "ipv4", &dvllist, NULL);
 		if (ret < 0) {
+			if (ret == -ENODATA || ret == -EAGAIN || ret == -ENOKEY)
+				/* translate these errors into something
+				 * userspace might understand */
+				ret = -EDESTADDRREQ;
 			_leave(" = %d", ret);
 			return ERR_PTR(ret);
 		}
···
 }
 
 /*
- * create a cell record
- * - "name" is the name of the cell
- * - "vllist" is a colon separated list of IP addresses in "a.b.c.d" format
+ * afs_cell_crate() - create a cell record
+ * @name:	is the name of the cell.
+ * @namsesz:	is the strlen of the cell name.
+ * @vllist:	is a colon separated list of IP addresses in "a.b.c.d" format.
+ * @retref:	is T to return the cell reference when the cell exists.
  */
-struct afs_cell *afs_cell_create(const char *name, char *vllist)
+struct afs_cell *afs_cell_create(const char *name, unsigned namesz,
+				 char *vllist, bool retref)
 {
 	struct afs_cell *cell;
 	int ret;
 
-	_enter("%s,%s", name, vllist);
+	_enter("%*.*s,%s", namesz, namesz, name ?: "", vllist);
 
 	down_write(&afs_cells_sem);
 	read_lock(&afs_cells_lock);
 	list_for_each_entry(cell, &afs_cells, link) {
-		if (strcasecmp(cell->name, name) == 0)
+		if (strncasecmp(cell->name, name, namesz) == 0)
 			goto duplicate_name;
 	}
 	read_unlock(&afs_cells_lock);
 
-	cell = afs_cell_alloc(name, vllist);
+	cell = afs_cell_alloc(name, namesz, vllist);
 	if (IS_ERR(cell)) {
 		_leave(" = %ld", PTR_ERR(cell));
 		up_write(&afs_cells_sem);
···
 	return ERR_PTR(ret);
 
 duplicate_name:
+	if (retref && !IS_ERR(cell))
+		afs_get_cell(cell);
+
 	read_unlock(&afs_cells_lock);
 	up_write(&afs_cells_sem);
+
+	if (retref) {
+		_leave(" = %p", cell);
+		return cell;
+	}
+
+	_leave(" = -EEXIST");
 	return ERR_PTR(-EEXIST);
 }
 
···
 		*cp++ = 0;
 
 	/* allocate a cell record for the root cell */
-	new_root = afs_cell_create(rootcell, cp);
+	new_root = afs_cell_create(rootcell, strlen(rootcell), cp, false);
 	if (IS_ERR(new_root)) {
 		_leave(" = %ld", PTR_ERR(new_root));
 		return PTR_ERR(new_root);
···
 /*
  * lookup a cell record
  */
-struct afs_cell *afs_cell_lookup(const char *name, unsigned namesz)
+struct afs_cell *afs_cell_lookup(const char *name, unsigned namesz,
+				 bool dns_cell)
 {
 	struct afs_cell *cell;
 
-	_enter("\"%*.*s\",", namesz, namesz, name ? name : "");
+	_enter("\"%*.*s\",", namesz, namesz, name ?: "");
 
 	down_read(&afs_cells_sem);
 	read_lock(&afs_cells_lock);
···
 			}
 		}
 		cell = ERR_PTR(-ENOENT);
+		if (dns_cell)
+			goto create_cell;
 	found:
 		;
 	} else {
···
 
 	read_unlock(&afs_cells_lock);
 	up_read(&afs_cells_sem);
+	_leave(" = %p", cell);
+	return cell;
+
+create_cell:
+	read_unlock(&afs_cells_lock);
+	up_read(&afs_cells_sem);
+
+	cell = afs_cell_create(name, namesz, NULL, true);
+
 	_leave(" = %p", cell);
 	return cell;
 }

fs/afs/dir.c

···
 }
 
 /*
+ * Try to auto mount the mountpoint with pseudo directory, if the autocell
+ * operation is setted.
+ */
+static struct inode *afs_try_auto_mntpt(
+	int ret, struct dentry *dentry, struct inode *dir, struct key *key,
+	struct afs_fid *fid)
+{
+	const char *devname = dentry->d_name.name;
+	struct afs_vnode *vnode = AFS_FS_I(dir);
+	struct inode *inode;
+
+	_enter("%d, %p{%s}, {%x:%u}, %p",
+	       ret, dentry, devname, vnode->fid.vid, vnode->fid.vnode, key);
+
+	if (ret != -ENOENT ||
+	    !test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
+		goto out;
+
+	inode = afs_iget_autocell(dir, devname, strlen(devname), key);
+	if (IS_ERR(inode)) {
+		ret = PTR_ERR(inode);
+		goto out;
+	}
+
+	*fid = AFS_FS_I(inode)->fid;
+	_leave("= %p", inode);
+	return inode;
+
+out:
+	_leave("= %d", ret);
+	return ERR_PTR(ret);
+}
+
+/*
  * look up an entry in a directory
  */
 static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
···
 
 	ret = afs_do_lookup(dir, dentry, &fid, key);
 	if (ret < 0) {
+		inode = afs_try_auto_mntpt(ret, dentry, dir, key, &fid);
+		if (!IS_ERR(inode)) {
+			key_put(key);
+			goto success;
+		}
+
+		ret = PTR_ERR(inode);
 		key_put(key);
 		if (ret == -ENOENT) {
 			d_add(dentry, NULL);
···
 		return ERR_CAST(inode);
 	}
 
+success:
 	dentry->d_op = &afs_fs_dentry_operations;
 
 	d_add(dentry, inode);
···
 		goto zap;
 
 	if (dentry->d_inode &&
-	    test_bit(AFS_VNODE_DELETED, &AFS_FS_I(dentry->d_inode)->flags))
-			goto zap;
+	    (test_bit(AFS_VNODE_DELETED,   &AFS_FS_I(dentry->d_inode)->flags) ||
+	     test_bit(AFS_VNODE_PSEUDODIR, &AFS_FS_I(dentry->d_inode)->flags)))
+		goto zap;
 
 	_leave(" = 0 [keep]");
 	return 0;

fs/afs/inode.c

···
 #include <linux/fs.h>
 #include <linux/pagemap.h>
 #include <linux/sched.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
 #include "internal.h"
 
 struct afs_iget_data {
···
 }
 
 /*
+ * iget5() comparator for inode created by autocell operations
+ *
+ * These pseudo inodes don't match anything.
+ */
+static int afs_iget5_autocell_test(struct inode *inode, void *opaque)
+{
+	return 0;
+}
+
+/*
  * iget5() inode initialiser
  */
 static int afs_iget5_set(struct inode *inode, void *opaque)
···
 	vnode->volume = data->volume;
 
 	return 0;
+}
+
+/*
+ * inode retrieval for autocell
+ */
+struct inode *afs_iget_autocell(struct inode *dir, const char *dev_name,
+				int namesz, struct key *key)
+{
+	struct afs_iget_data data;
+	struct afs_super_info *as;
+	struct afs_vnode *vnode;
+	struct super_block *sb;
+	struct inode *inode;
+	static atomic_t afs_autocell_ino;
+
+	_enter("{%x:%u},%*.*s,",
+	       AFS_FS_I(dir)->fid.vid, AFS_FS_I(dir)->fid.vnode,
+	       namesz, namesz, dev_name ?: "");
+
+	sb = dir->i_sb;
+	as = sb->s_fs_info;
+	data.volume = as->volume;
+	data.fid.vid = as->volume->vid;
+	data.fid.unique = 0;
+	data.fid.vnode = 0;
+
+	inode = iget5_locked(sb, atomic_inc_return(&afs_autocell_ino),
+			     afs_iget5_autocell_test, afs_iget5_set,
+			     &data);
+	if (!inode) {
+		_leave(" = -ENOMEM");
+		return ERR_PTR(-ENOMEM);
+	}
+
+	_debug("GOT INODE %p { ino=%lu, vl=%x, vn=%x, u=%x }",
+	       inode, inode->i_ino, data.fid.vid, data.fid.vnode,
+	       data.fid.unique);
+
+	vnode = AFS_FS_I(inode);
+
+	/* there shouldn't be an existing inode */
+	BUG_ON(!(inode->i_state & I_NEW));
+
+	inode->i_size		= 0;
+	inode->i_mode		= S_IFDIR | S_IRUGO | S_IXUGO;
+	inode->i_op		= &afs_autocell_inode_operations;
+	inode->i_nlink		= 2;
+	inode->i_uid		= 0;
+	inode->i_gid		= 0;
+	inode->i_ctime.tv_sec	= get_seconds();
+	inode->i_ctime.tv_nsec	= 0;
+	inode->i_atime		= inode->i_mtime = inode->i_ctime;
+	inode->i_blocks		= 0;
+	inode->i_version	= 0;
+	inode->i_generation	= 0;
+
+	set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
+	inode->i_flags |= S_NOATIME;
+	unlock_new_inode(inode);
+	_leave(" = %p", inode);
+	return inode;
 }
 
 /*
···
 
 	generic_fillattr(inode, stat);
 	return 0;
+}
+
+/*
+ * discard an AFS inode
+ */
+int afs_drop_inode(struct inode *inode)
+{
+	_enter("");
+
+	if (test_bit(AFS_VNODE_PSEUDODIR, &AFS_FS_I(inode)->flags))
+		return generic_delete_inode(inode);
+	else
+		return generic_drop_inode(inode);
 }
 
 /*

fs/afs/internal.h

···
 struct afs_mount_params {
 	bool			rwpath;		/* T if the parent should be considered R/W */
 	bool			force;		/* T to force cell type */
+	bool			autocell;	/* T if set auto mount operation */
 	afs_voltype_t		type;		/* type of volume requested */
 	int			volnamesz;	/* size of volume name */
 	const char		*volname;	/* name of volume to mount */
···
 #define AFS_VNODE_READLOCKED	7		/* set if vnode is read-locked on the server */
 #define AFS_VNODE_WRITELOCKED	8		/* set if vnode is write-locked on the server */
 #define AFS_VNODE_UNLOCKING	9		/* set if vnode is being unlocked on the server */
+#define AFS_VNODE_AUTOCELL	10		/* set if Vnode is an auto mount point */
+#define AFS_VNODE_PSEUDODIR	11		/* set if Vnode is a pseudo directory */
 
 	long			acl_order;	/* ACL check count (callback break count) */
 
···
 
 #define afs_get_cell(C) do { atomic_inc(&(C)->usage); } while(0)
 extern int afs_cell_init(char *);
-extern struct afs_cell *afs_cell_create(const char *, char *);
-extern struct afs_cell *afs_cell_lookup(const char *, unsigned);
+extern struct afs_cell *afs_cell_create(const char *, unsigned, char *, bool);
+extern struct afs_cell *afs_cell_lookup(const char *, unsigned, bool);
 extern struct afs_cell *afs_grab_cell(struct afs_cell *);
 extern void afs_put_cell(struct afs_cell *);
 extern void afs_cell_purge(void);
···
 /*
  * inode.c
  */
+extern struct inode *afs_iget_autocell(struct inode *, const char *, int,
+				       struct key *);
 extern struct inode *afs_iget(struct super_block *, struct key *,
 			      struct afs_fid *, struct afs_file_status *,
 			      struct afs_callback *);
···
 extern int afs_getattr(struct vfsmount *, struct dentry *, struct kstat *);
 extern int afs_setattr(struct dentry *, struct iattr *);
 extern void afs_evict_inode(struct inode *);
+extern int afs_drop_inode(struct inode *);
 
 /*
  * main.c
···
  * mntpt.c
  */
 extern const struct inode_operations afs_mntpt_inode_operations;
+extern const struct inode_operations afs_autocell_inode_operations;
 extern const struct file_operations afs_mntpt_file_operations;
 
 extern int afs_mntpt_check_symlink(struct afs_vnode *, struct key *);

fs/afs/mntpt.c

···
 	.getattr	= afs_getattr,
 };
 
+const struct inode_operations afs_autocell_inode_operations = {
+	.follow_link	= afs_mntpt_follow_link,
+	.getattr	= afs_getattr,
+};
+
 static LIST_HEAD(afs_vfsmounts);
 static DECLARE_DELAYED_WORK(afs_mntpt_expiry_timer, afs_mntpt_expiry_timed_out);
 
···
 {
 	struct afs_super_info *super;
 	struct vfsmount *mnt;
+	struct afs_vnode *vnode;
 	struct page *page;
-	size_t size;
-	char *buf, *devname, *options;
+	char *devname, *options;
+	bool rwpath = false;
 	int ret;
 
 	_enter("{%s}", mntpt->d_name.name);
 
 	BUG_ON(!mntpt->d_inode);
-
-	ret = -EINVAL;
-	size = mntpt->d_inode->i_size;
-	if (size > PAGE_SIZE - 1)
-		goto error_no_devname;
 
 	ret = -ENOMEM;
 	devname = (char *) get_zeroed_page(GFP_KERNEL);
···
 	if (!options)
 		goto error_no_options;
 
-	/* read the contents of the AFS special symlink */
-	page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
-	if (IS_ERR(page)) {
-		ret = PTR_ERR(page);
-		goto error_no_page;
+	vnode = AFS_FS_I(mntpt->d_inode);
+	if (test_bit(AFS_VNODE_PSEUDODIR, &vnode->flags)) {
+		/* if the directory is a pseudo directory, use the d_name */
+		static const char afs_root_cell[] = ":root.cell.";
+		unsigned size = mntpt->d_name.len;
+
+		ret = -ENOENT;
+		if (size < 2 || size > AFS_MAXCELLNAME)
+			goto error_no_page;
+
+		if (mntpt->d_name.name[0] == '.') {
+			devname[0] = '#';
+			memcpy(devname + 1, mntpt->d_name.name, size - 1);
+			memcpy(devname + size, afs_root_cell,
+			       sizeof(afs_root_cell));
+			rwpath = true;
+		} else {
+			devname[0] = '%';
+			memcpy(devname + 1, mntpt->d_name.name, size);
+			memcpy(devname + size + 1, afs_root_cell,
+			       sizeof(afs_root_cell));
+		}
+	} else {
+		/* read the contents of the AFS special symlink */
+		loff_t size = i_size_read(mntpt->d_inode);
+		char *buf;
+
+		ret = -EINVAL;
+		if (size > PAGE_SIZE - 1)
+			goto error_no_page;
+
+		page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
+		if (IS_ERR(page)) {
+			ret = PTR_ERR(page);
+			goto error_no_page;
+		}
+
+		ret = -EIO;
+		if (PageError(page))
+			goto error;
+
+		buf = kmap_atomic(page, KM_USER0);
+		memcpy(devname, buf, size);
+		kunmap_atomic(buf, KM_USER0);
+		page_cache_release(page);
+		page = NULL;
 	}
-
-	ret = -EIO;
-	if (PageError(page))
-		goto error;
-
-	buf = kmap_atomic(page, KM_USER0);
-	memcpy(devname, buf, size);
-	kunmap_atomic(buf, KM_USER0);
-	page_cache_release(page);
-	page = NULL;
 
 	/* work out what options we want */
 	super = AFS_FS_S(mntpt->d_sb);
 	memcpy(options, "cell=", 5);
 	strcpy(options + 5, super->volume->cell->name);
-	if (super->volume->type == AFSVL_RWVOL)
+	if (super->volume->type == AFSVL_RWVOL || rwpath)
 		strcat(options, ",rwpath");
 
 	/* try and do the mount */

fs/afs/proc.c

···
 	if (strcmp(kbuf, "add") == 0) {
 		struct afs_cell *cell;
 
-		cell = afs_cell_create(name, args);
+		cell = afs_cell_create(name, strlen(name), args, false);
 		if (IS_ERR(cell)) {
 			ret = PTR_ERR(cell);
 			goto done;

fs/afs/super.c

···
 
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/mount.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/smp_lock.h>
···
 static const struct super_operations afs_super_ops = {
 	.statfs		= afs_statfs,
 	.alloc_inode	= afs_alloc_inode,
+	.drop_inode	= afs_drop_inode,
 	.destroy_inode	= afs_destroy_inode,
 	.evict_inode	= afs_evict_inode,
 	.put_super	= afs_put_super,
···
 	afs_opt_cell,
 	afs_opt_rwpath,
 	afs_opt_vol,
+	afs_opt_autocell,
 };
 
 static const match_table_t afs_options_list = {
 	{ afs_opt_cell,		"cell=%s"	},
 	{ afs_opt_rwpath,	"rwpath"	},
 	{ afs_opt_vol,		"vol=%s"	},
+	{ afs_opt_autocell,	"autocell"	},
 	{ afs_no_opt,		NULL		},
 };
 
···
 		switch (token) {
 		case afs_opt_cell:
 			cell = afs_cell_lookup(args[0].from,
-					       args[0].to - args[0].from);
+					       args[0].to - args[0].from,
+					       false);
 			if (IS_ERR(cell))
 				return PTR_ERR(cell);
 			afs_put_cell(params->cell);
···
 
 		case afs_opt_vol:
 			*devname = args[0].from;
+			break;
+
+		case afs_opt_autocell:
+			params->autocell = 1;
 			break;
 
 		default:
···
 
 	/* lookup the cell record */
 	if (cellname || !params->cell) {
-		cell = afs_cell_lookup(cellname, cellnamesz);
+		cell = afs_cell_lookup(cellname, cellnamesz, true);
 		if (IS_ERR(cell)) {
-			printk(KERN_ERR "kAFS: unable to lookup cell '%s'\n",
-			       cellname ?: "");
+			printk(KERN_ERR "kAFS: unable to lookup cell '%*.*s'\n",
+			       cellnamesz, cellnamesz, cellname ?: "");
 			return PTR_ERR(cell);
 		}
 		afs_put_cell(params->cell);
···
 	inode = afs_iget(sb, params->key, &fid, NULL, NULL);
 	if (IS_ERR(inode))
 		goto error_inode;
+
+	if (params->autocell)
+		set_bit(AFS_VNODE_AUTOCELL, &AFS_FS_I(inode)->flags);
 
 	ret = -ENOMEM;
 	root = d_alloc_root(inode);

fs/cifs/README

···
   gid		Set the default gid for inodes (similar to above).
   file_mode     If CIFS Unix extensions are not supported by the server
 		this overrides the default mode for file inodes.
+  fsc		Enable local disk caching using FS-Cache (off by default). This
+  		option could be useful to improve performance on a slow link,
+		heavily loaded server and/or network where reading from the
+		disk is faster than reading from the server (over the network).
+		This could also impact scalability positively as the
+		number of calls to the server are reduced. However, local
+		caching is not suitable for all workloads for e.g. read-once
+		type workloads. So, you need to consider carefully your
+		workload/scenario before using this option. Currently, local
+		disk caching is functional for CIFS files opened as read-only.
   dir_mode      If CIFS Unix extensions are not supported by the server 
 		this overrides the default mode for directory inodes.
   port		attempt to contact the server on this tcp port, before

fs/nfs/Kconfig

···
 	help
 	  Say Y here if you want NFS data to be cached locally on disc through
 	  the general filesystem cache manager
+
+config NFS_USE_LEGACY_DNS
+	bool "Use the legacy NFS DNS resolver"
+	depends on NFS_V4
+	help
+	  The kernel now provides a method for translating a host name into an
+	  IP address.  Select Y here if you would rather use your own DNS
+	  resolver script.
+
+	  If unsure, say N
+
+config NFS_USE_KERNEL_DNS
+	bool
+	depends on NFS_V4 && !NFS_USE_LEGACY_DNS
+	select DNS_RESOLVER
+	select KEYS
+	default y

fs/nfs/dns_resolve.c

···
  * Resolves DNS hostnames into valid ip addresses
  */
 
+#ifdef CONFIG_NFS_USE_KERNEL_DNS
+
+#include <linux/sunrpc/clnt.h>
+#include <linux/dns_resolver.h>
+
+ssize_t nfs_dns_resolve_name(char *name, size_t namelen,
+		struct sockaddr *sa, size_t salen)
+{
+	ssize_t ret;
+	char *ip_addr = NULL;
+	int ip_len;
+
+	ip_len = dns_query(NULL, name, namelen, NULL, &ip_addr, NULL);
+	if (ip_len > 0)
+		ret = rpc_pton(ip_addr, ip_len, sa, salen);
+	else
+		ret = -ESRCH;
+	kfree(ip_addr);
+	return ret;
+}
+
+#else
+
 #include <linux/hash.h>
 #include <linux/string.h>
 #include <linux/kmod.h>
···
 	nfs_cache_unregister(&nfs_dns_resolve);
 }
 
+#endif

fs/nfs/dns_resolve.h

···
 
 #define NFS_DNS_HOSTNAME_MAXLEN	(128)
 
+
+#ifdef CONFIG_NFS_USE_KERNEL_DNS
+static inline int nfs_dns_resolver_init(void)
+{
+	return 0;
+}
+
+static inline void nfs_dns_resolver_destroy(void)
+{}
+#else
 extern int nfs_dns_resolver_init(void);
 extern void nfs_dns_resolver_destroy(void);
+#endif
+
 extern ssize_t nfs_dns_resolve_name(char *name, size_t namelen,
 		struct sockaddr *sa, size_t salen);
 

net/dns_resolver/dns_key.c

···
 #include <linux/kernel.h>
 #include <linux/keyctl.h>
 #include <linux/err.h>
+#include <linux/seq_file.h>
 #include <keys/dns_resolver-type.h>
 #include <keys/user-type.h>
 #include "internal.h"
···
 MODULE_PARM_DESC(debug, "DNS Resolver debugging mask");
 
 const struct cred *dns_resolver_cache;
+
+#define	DNS_ERRORNO_OPTION	"dnserror"
 
 /*
  * Instantiate a user defined key for dns_resolver.
···
 dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen)
 {
 	struct user_key_payload *upayload;
+	unsigned long derrno;
 	int ret;
 	size_t result_len = 0;
-	const char *data = _data, *opt;
+	const char *data = _data, *end, *opt;
 
 	kenter("%%%d,%s,'%s',%zu",
 	       key->serial, key->description, data, datalen);
···
 	datalen--;
 
 	/* deal with any options embedded in the data */
+	end = data + datalen;
 	opt = memchr(data, '#', datalen);
 	if (!opt) {
-		kdebug("no options currently supported");
-		return -EINVAL;
+		/* no options: the entire data is the result */
+		kdebug("no options");
+		result_len = datalen;
+	} else {
+		const char *next_opt;
+
+		result_len = opt - data;
+		opt++;
+		kdebug("options: '%s'", opt);
+		do {
+			const char *eq;
+			int opt_len, opt_nlen, opt_vlen, tmp;
+
+			next_opt = memchr(opt, '#', end - opt) ?: end;
+			opt_len = next_opt - opt;
+			if (!opt_len) {
+				printk(KERN_WARNING
+				       "Empty option to dns_resolver key %d\n",
+				       key->serial);
+				return -EINVAL;
+			}
+
+			eq = memchr(opt, '=', opt_len) ?: end;
+			opt_nlen = eq - opt;
+			eq++;
+			opt_vlen = next_opt - eq; /* will be -1 if no value */
+
+			tmp = opt_vlen >= 0 ? opt_vlen : 0;
+			kdebug("option '%*.*s' val '%*.*s'",
+			       opt_nlen, opt_nlen, opt, tmp, tmp, eq);
+
+			/* see if it's an error number representing a DNS error
+			 * that's to be recorded as the result in this key */
+			if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 &&
+			    memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) {
+				kdebug("dns error number option");
+				if (opt_vlen <= 0)
+					goto bad_option_value;
+
+				ret = strict_strtoul(eq, 10, &derrno);
+				if (ret < 0)
+					goto bad_option_value;
+
+				if (derrno < 1 || derrno > 511)
+					goto bad_option_value;
+
+				kdebug("dns error no. = %lu", derrno);
+				key->type_data.x[0] = -derrno;
+				continue;
+			}
+
+		bad_option_value:
+			printk(KERN_WARNING
+			       "Option '%*.*s' to dns_resolver key %d:"
+			       " bad/missing value\n",
+			       opt_nlen, opt_nlen, opt, key->serial);
+			return -EINVAL;
+		} while (opt = next_opt + 1, opt < end);
 	}
 
-	result_len = datalen;
+	/* don't cache the result if we're caching an error saying there's no
+	 * result */
+	if (key->type_data.x[0]) {
+		kleave(" = 0 [h_error %ld]", key->type_data.x[0]);
+		return 0;
+	}
+
+	kdebug("store result");
 	ret = key_payload_reserve(key, result_len);
 	if (ret < 0)
 		return -EINVAL;
···
 	return ret;
 }
 
+/*
+ * Describe a DNS key
+ */
+static void dns_resolver_describe(const struct key *key, struct seq_file *m)
+{
+	int err = key->type_data.x[0];
+
+	seq_puts(m, key->description);
+	if (err)
+		seq_printf(m, ": %d", err);
+	else
+		seq_printf(m, ": %u", key->datalen);
+}
+
 struct key_type key_type_dns_resolver = {
 	.name		= "dns_resolver",
 	.instantiate	= dns_resolver_instantiate,
 	.match		= dns_resolver_match,
 	.revoke		= user_revoke,
 	.destroy	= user_destroy,
-	.describe	= user_describe,
+	.describe	= dns_resolver_describe,
 	.read		= user_read,
 };
 

net/dns_resolver/dns_query.c

···
 	if (ret < 0)
 		goto put;
 
+	/* If the DNS server gave an error, return that to the caller */
+	ret = rkey->type_data.x[0];
+	if (ret)
+		goto put;
+
 	upayload = rcu_dereference_protected(rkey->payload.data,
 					     lockdep_is_held(&rkey->sem));
 	len = upayload->datalen;