fat (exportfs): fix dentry reconnection

Maintain an index of directory inodes by starting cluster, so that
fat_get_parent() can return the proper cached inode rather than inventing
one that cannot be traced back to the filesystem root.

Add a new msdos/vfat binary mount option "nfs" so that FAT filesystems
that are _not_ exported via NFS are not saddled with maintenance of an
index they will never use.

Finally, simplify NFS file handle generation and lookups.  An
ext2-congruent implementation is adequate for FAT needs.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 141 insertions, 137 deletions

diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index d70d8f31f704..55e088cc0613 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -872,21 +872,23 @@ static int fat_get_short_entry(struct inode *dir, loff_t *pos,
 }
 
 /*
- * The ".." entry can not provide the "struct fat_slot_info" informations
- * for inode. So, this function provide the some informations only.
+ * The ".." entry can not provide the "struct fat_slot_info" information
+ * for inode, nor a usable i_pos. So, this function provides some information
+ * only.
+ *
+ * Since this function walks through the on-disk inodes within a directory,
+ * callers are responsible for taking any locks necessary to prevent the
+ * directory from changing.
  */
 int fat_get_dotdot_entry(struct inode *dir, struct buffer_head **bh,
-                         struct msdos_dir_entry **de, loff_t *i_pos)
+                         struct msdos_dir_entry **de)
 {
-        loff_t offset;
+        loff_t offset = 0;
 
-        offset = 0;
-        *bh = NULL;
+        *de = NULL;
         while (fat_get_short_entry(dir, &offset, bh, de) >= 0) {
-                if (!strncmp((*de)->name, MSDOS_DOTDOT, MSDOS_NAME)) {
-                        *i_pos = fat_make_i_pos(dir->i_sb, *bh, *de);
+                if (!strncmp((*de)->name, MSDOS_DOTDOT, MSDOS_NAME))
                         return 0;
-                }
         }
         return -ENOENT;
 }
diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index fb95939ff870..ec54c3a7f2f7 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -5,6 +5,7 @@
 #include <linux/string.h>
 #include <linux/nls.h>
 #include <linux/fs.h>
+#include <linux/hash.h>
 #include <linux/mutex.h>
 #include <linux/ratelimit.h>
 #include <linux/msdos_fs.h>
@@ -46,7 +47,8 @@ struct fat_mount_options {
                  usefree:1,       /* Use free_clusters for FAT32 */
                  tz_utc:1,        /* Filesystem timestamps are in UTC */
                  rodir:1,         /* allow ATTR_RO for directory */
-                 discard:1;       /* Issue discard requests on deletions */
+                 discard:1,       /* Issue discard requests on deletions */
+                 nfs:1;           /* Do extra work needed for NFS export */
 };
 
 #define FAT_HASH_BITS   8
@@ -88,6 +90,9 @@ struct msdos_sb_info {
 
         spinlock_t inode_hash_lock;
         struct hlist_head inode_hashtable[FAT_HASH_SIZE];
+
+        spinlock_t dir_hash_lock;
+        struct hlist_head dir_hashtable[FAT_HASH_SIZE];
 };
 
 #define FAT_CACHE_VALID 0       /* special case for valid cache */
@@ -110,6 +115,7 @@ struct msdos_inode_info {
         int i_attrs;            /* unused attribute bits */
         loff_t i_pos;           /* on-disk position of directory entry or 0 */
         struct hlist_node i_fat_hash;   /* hash by i_location */
+        struct hlist_node i_dir_hash;   /* hash by i_logstart */
         struct rw_semaphore truncate_lock; /* protect bmap against truncate */
         struct inode vfs_inode;
 };
@@ -262,7 +268,7 @@ extern int fat_subdirs(struct inode *dir);
 extern int fat_scan(struct inode *dir, const unsigned char *name,
                     struct fat_slot_info *sinfo);
 extern int fat_get_dotdot_entry(struct inode *dir, struct buffer_head **bh,
-                                struct msdos_dir_entry **de, loff_t *i_pos);
+                                struct msdos_dir_entry **de);
 extern int fat_alloc_new_dir(struct inode *dir, struct timespec *ts);
 extern int fat_add_entries(struct inode *dir, void *slots, int nr_slots,
                            struct fat_slot_info *sinfo);
@@ -341,18 +347,9 @@ extern int fat_fill_super(struct super_block *sb, void *data, int silent,
 
 extern int fat_flush_inodes(struct super_block *sb, struct inode *i1,
                             struct inode *i2);
-static inline loff_t fat_i_pos_read(struct msdos_sb_info *sbi,
-                                    struct inode *inode)
+static inline unsigned long fat_dir_hash(int logstart)
 {
-        loff_t i_pos;
-#if BITS_PER_LONG == 32
-        spin_lock(&sbi->inode_hash_lock);
-#endif
-        i_pos = MSDOS_I(inode)->i_pos;
-#if BITS_PER_LONG == 32
-        spin_unlock(&sbi->inode_hash_lock);
-#endif
-        return i_pos;
+        return hash_32(logstart, FAT_HASH_BITS);
 }
 
 /* fat/misc.c */
@@ -382,10 +379,10 @@ void fat_cache_destroy(void);
 
 /* fat/nfs.c */
 struct fid;
-extern int fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp,
-                         struct inode *parent);
 extern struct dentry *fat_fh_to_dentry(struct super_block *sb, struct fid *fid,
                                        int fh_len, int fh_type);
+extern struct dentry *fat_fh_to_parent(struct super_block *sb, struct fid *fid,
+                                       int fh_len, int fh_type);
 extern struct dentry *fat_get_parent(struct dentry *child_dir);
 
 /* helper for printk */
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 169f6ebddf96..5741b11650f1 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -281,15 +281,42 @@ static inline unsigned long fat_hash(loff_t i_pos)
         return hash_32(i_pos, FAT_HASH_BITS);
 }
 
+static void dir_hash_init(struct super_block *sb)
+{
+        struct msdos_sb_info *sbi = MSDOS_SB(sb);
+        int i;
+
+        spin_lock_init(&sbi->dir_hash_lock);
+        for (i = 0; i < FAT_HASH_SIZE; i++)
+                INIT_HLIST_HEAD(&sbi->dir_hashtable[i]);
+}
+
 void fat_attach(struct inode *inode, loff_t i_pos)
 {
         struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
-        struct hlist_head *head = sbi->inode_hashtable + fat_hash(i_pos);
 
-        spin_lock(&sbi->inode_hash_lock);
-        MSDOS_I(inode)->i_pos = i_pos;
-        hlist_add_head(&MSDOS_I(inode)->i_fat_hash, head);
-        spin_unlock(&sbi->inode_hash_lock);
+        if (inode->i_ino != MSDOS_ROOT_INO) {
+                struct hlist_head *head =   sbi->inode_hashtable
+                                          + fat_hash(i_pos);
+
+                spin_lock(&sbi->inode_hash_lock);
+                MSDOS_I(inode)->i_pos = i_pos;
+                hlist_add_head(&MSDOS_I(inode)->i_fat_hash, head);
+                spin_unlock(&sbi->inode_hash_lock);
+        }
+
+        /* If NFS support is enabled, cache the mapping of start cluster
+         * to directory inode. This is used during reconnection of
+         * dentries to the filesystem root.
+         */
+        if (S_ISDIR(inode->i_mode) && sbi->options.nfs) {
+                struct hlist_head *d_head = sbi->dir_hashtable;
+                d_head += fat_dir_hash(MSDOS_I(inode)->i_logstart);
+
+                spin_lock(&sbi->dir_hash_lock);
+                hlist_add_head(&MSDOS_I(inode)->i_dir_hash, d_head);
+                spin_unlock(&sbi->dir_hash_lock);
+        }
 }
 EXPORT_SYMBOL_GPL(fat_attach);
 
@@ -300,6 +327,12 @@ void fat_detach(struct inode *inode)
         MSDOS_I(inode)->i_pos = 0;
         hlist_del_init(&MSDOS_I(inode)->i_fat_hash);
         spin_unlock(&sbi->inode_hash_lock);
+
+        if (S_ISDIR(inode->i_mode) && sbi->options.nfs) {
+                spin_lock(&sbi->dir_hash_lock);
+                hlist_del_init(&MSDOS_I(inode)->i_dir_hash);
+                spin_unlock(&sbi->dir_hash_lock);
+        }
 }
 EXPORT_SYMBOL_GPL(fat_detach);
 
@@ -504,6 +537,7 @@ static void init_once(void *foo)
         ei->cache_valid_id = FAT_CACHE_VALID + 1;
         INIT_LIST_HEAD(&ei->cache_lru);
         INIT_HLIST_NODE(&ei->i_fat_hash);
+        INIT_HLIST_NODE(&ei->i_dir_hash);
         inode_init_once(&ei->vfs_inode);
 }
 
@@ -562,6 +596,20 @@ static int fat_statfs(struct dentry *dentry, struct kstatfs *buf)
         return 0;
 }
 
+static inline loff_t fat_i_pos_read(struct msdos_sb_info *sbi,
+                                    struct inode *inode)
+{
+        loff_t i_pos;
+#if BITS_PER_LONG == 32
+        spin_lock(&sbi->inode_hash_lock);
+#endif
+        i_pos = MSDOS_I(inode)->i_pos;
+#if BITS_PER_LONG == 32
+        spin_unlock(&sbi->inode_hash_lock);
+#endif
+        return i_pos;
+}
+
 static int __fat_write_inode(struct inode *inode, int wait)
 {
         struct super_block *sb = inode->i_sb;
@@ -655,8 +703,8 @@ static const struct super_operations fat_sops = {
 };
 
 static const struct export_operations fat_export_ops = {
-        .encode_fh      = fat_encode_fh,
         .fh_to_dentry   = fat_fh_to_dentry,
+        .fh_to_parent   = fat_fh_to_parent,
         .get_parent     = fat_get_parent,
 };
 
@@ -706,6 +754,8 @@ static int fat_show_options(struct seq_file *m, struct dentry *root)
                 seq_puts(m, ",usefree");
         if (opts->quiet)
                 seq_puts(m, ",quiet");
+        if (opts->nfs)
+                seq_puts(m, ",nfs");
         if (opts->showexec)
                 seq_puts(m, ",showexec");
         if (opts->sys_immutable)
@@ -750,7 +800,7 @@ enum {
         Opt_shortname_winnt, Opt_shortname_mixed, Opt_utf8_no, Opt_utf8_yes,
         Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,
         Opt_obsolete, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,
-        Opt_err_panic, Opt_err_ro, Opt_discard, Opt_err,
+        Opt_err_panic, Opt_err_ro, Opt_discard, Opt_nfs, Opt_err,
 };
 
 static const match_table_t fat_tokens = {
@@ -779,6 +829,7 @@ static const match_table_t fat_tokens = {
         {Opt_err_panic, "errors=panic"},
         {Opt_err_ro, "errors=remount-ro"},
         {Opt_discard, "discard"},
+        {Opt_nfs, "nfs"},
         {Opt_obsolete, "conv=binary"},
         {Opt_obsolete, "conv=text"},
         {Opt_obsolete, "conv=auto"},
@@ -859,6 +910,7 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
         opts->numtail = 1;
         opts->usefree = opts->nocase = 0;
         opts->tz_utc = 0;
+        opts->nfs = 0;
         opts->errors = FAT_ERRORS_RO;
         *debug = 0;
 
@@ -1023,6 +1075,9 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
                 case Opt_discard:
                         opts->discard = 1;
                         break;
+                case Opt_nfs:
+                        opts->nfs = 1;
+                        break;
 
                 /* obsolete mount options */
                 case Opt_obsolete:
@@ -1313,6 +1368,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 
         /* set up enough so that it can read an inode */
         fat_hash_init(sb);
+        dir_hash_init(sb);
         fat_ent_access_init(sb);
 
         /*
@@ -1367,6 +1423,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
         }
         error = -ENOMEM;
         insert_inode_hash(root_inode);
+        fat_attach(root_inode, 0);
         sb->s_root = d_make_root(root_inode);
         if (!sb->s_root) {
                 fat_msg(sb, KERN_ERR, "get root inode failed");
diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index b0e12bf9f4a1..c27c63020292 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -440,7 +440,7 @@ static int do_msdos_rename(struct inode *old_dir, unsigned char *old_name,
         struct inode *old_inode, *new_inode;
         struct fat_slot_info old_sinfo, sinfo;
         struct timespec ts;
-        loff_t dotdot_i_pos, new_i_pos;
+        loff_t new_i_pos;
         int err, old_attrs, is_dir, update_dotdot, corrupt = 0;
 
         old_sinfo.bh = sinfo.bh = dotdot_bh = NULL;
@@ -456,8 +456,7 @@ static int do_msdos_rename(struct inode *old_dir, unsigned char *old_name,
         is_dir = S_ISDIR(old_inode->i_mode);
         update_dotdot = (is_dir && old_dir != new_dir);
         if (update_dotdot) {
-                if (fat_get_dotdot_entry(old_inode, &dotdot_bh, &dotdot_de,
-                                         &dotdot_i_pos) < 0) {
+                if (fat_get_dotdot_entry(old_inode, &dotdot_bh, &dotdot_de)) {
                         err = -EIO;
                         goto out;
                 }
diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index 6a6d8c0715a1..e535dd75b986 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -914,7 +914,7 @@ static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
         struct inode *old_inode, *new_inode;
         struct fat_slot_info old_sinfo, sinfo;
         struct timespec ts;
-        loff_t dotdot_i_pos, new_i_pos;
+        loff_t new_i_pos;
         int err, is_dir, update_dotdot, corrupt = 0;
         struct super_block *sb = old_dir->i_sb;
 
@@ -929,8 +929,7 @@ static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
         is_dir = S_ISDIR(old_inode->i_mode);
         update_dotdot = (is_dir && old_dir != new_dir);
         if (update_dotdot) {
-                if (fat_get_dotdot_entry(old_inode, &dotdot_bh, &dotdot_de,
-                                         &dotdot_i_pos) < 0) {
+                if (fat_get_dotdot_entry(old_inode, &dotdot_bh, &dotdot_de)) {
                         err = -EIO;
                         goto out;
                 }
diff --git a/fs/fat/nfs.c b/fs/fat/nfs.c
index 21609a1e9355..ef4b5faba87b 100644
--- a/fs/fat/nfs.c
+++ b/fs/fat/nfs.c
@@ -14,47 +14,46 @@
 #include <linux/exportfs.h>
 #include "fat.h"
 
-/*
- * a FAT file handle with fhtype 3 is
- *  0/  i_ino - for fast, reliable lookup if still in the cache
- *  1/  i_generation - to see if i_ino is still valid
- *          bit 0 == 0 iff directory
- *  2/  i_pos(8-39) - if ino has changed, but still in cache
- *  3/  i_pos(4-7)|i_logstart - to semi-verify inode found at i_pos
- *  4/  i_pos(0-3)|parent->i_logstart - maybe used to hunt for the file on disc
- *
- * Hack for NFSv2: Maximum FAT entry number is 28bits and maximum
- * i_pos is 40bits (blocknr(32) + dir offset(8)), so two 4bits
- * of i_logstart is used to store the directory entry offset.
+/**
+ * Look up a directory inode given its starting cluster.
  */
-
-int
-fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp, struct inode *parent)
+static struct inode *fat_dget(struct super_block *sb, int i_logstart)
 {
-        int len = *lenp;
-        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
-        loff_t i_pos;
+        struct msdos_sb_info *sbi = MSDOS_SB(sb);
+        struct hlist_head *head;
+        struct hlist_node *_p;
+        struct msdos_inode_info *i;
+        struct inode *inode = NULL;
 
-        if (len < 5) {
-                *lenp = 5;
-                return 255; /* no room */
+        head = sbi->dir_hashtable + fat_dir_hash(i_logstart);
+        spin_lock(&sbi->dir_hash_lock);
+        hlist_for_each_entry(i, _p, head, i_dir_hash) {
+                BUG_ON(i->vfs_inode.i_sb != sb);
+                if (i->i_logstart != i_logstart)
+                        continue;
+                inode = igrab(&i->vfs_inode);
+                if (inode)
+                        break;
         }
-
-        i_pos = fat_i_pos_read(sbi, inode);
-        *lenp = 5;
-        fh[0] = inode->i_ino;
-        fh[1] = inode->i_generation;
-        fh[2] = i_pos >> 8;
-        fh[3] = ((i_pos & 0xf0) << 24) | MSDOS_I(inode)->i_logstart;
-        fh[4] = (i_pos & 0x0f) << 28;
-        if (parent)
-                fh[4] |= MSDOS_I(parent)->i_logstart;
-        return 3;
+        spin_unlock(&sbi->dir_hash_lock);
+        return inode;
 }
 
-static int fat_is_valid_fh(int fh_len, int fh_type)
+static struct inode *fat_nfs_get_inode(struct super_block *sb,
+                                       u64 ino, u32 generation)
 {
-        return ((fh_len >= 5) && (fh_type == 3));
+        struct inode *inode;
+
+        if ((ino < MSDOS_ROOT_INO) || (ino == MSDOS_FSINFO_INO))
+                return NULL;
+
+        inode = ilookup(sb, ino);
+        if (inode && generation && (inode->i_generation != generation)) {
+                iput(inode);
+                inode = NULL;
+        }
+
+        return inode;
 }
 
 /**
@@ -64,57 +63,19 @@ static int fat_is_valid_fh(int fh_len, int fh_type)
 struct dentry *fat_fh_to_dentry(struct super_block *sb, struct fid *fid,
                                 int fh_len, int fh_type)
 {
-        struct inode *inode = NULL;
-        u32 *fh = fid->raw;
-        loff_t i_pos;
-        unsigned long i_ino;
-        __u32 i_generation;
-        int i_logstart;
-
-        if (!fat_is_valid_fh(fh_len, fh_type))
-                return NULL;
-
-        i_ino = fh[0];
-        i_generation = fh[1];
-        i_logstart = fh[3] & 0x0fffffff;
-
-        /* Try i_ino lookup first - fastest and most reliable */
-        inode = ilookup(sb, i_ino);
-        if (inode && (inode->i_generation != i_generation)) {
-                iput(inode);
-                inode = NULL;
-        }
-        if (!inode) {
-                i_pos = (loff_t)fh[2] << 8;
-                i_pos |= ((fh[3] >> 24) & 0xf0) | (fh[4] >> 28);
-
-                /* try 2 - see if i_pos is in F-d-c
-                 * require i_logstart to be the same
-                 * Will fail if you truncate and then re-write
-                 */
-
-                inode = fat_iget(sb, i_pos);
-                if (inode && MSDOS_I(inode)->i_logstart != i_logstart) {
-                        iput(inode);
-                        inode = NULL;
-                }
-        }
+        return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
+                                    fat_nfs_get_inode);
+}
 
-        /*
-         * For now, do nothing if the inode is not found.
-         *
-         * What we could do is:
-         *
-         *      - follow the file starting at fh[4], and record the ".." entry,
-         *        and the name of the fh[2] entry.
-         *      - then follow the ".." file finding the next step up.
-         *
-         * This way we build a path to the root of the tree. If this works, we
-         * lookup the path and so get this inode into the cache.  Finally try
-         * the fat_iget lookup again.  If that fails, then we are totally out
-         * of luck.  But all that is for another day
-         */
-        return d_obtain_alias(inode);
+/*
+ * Find the parent for a file specified by NFS handle.
+ * This requires that the handle contain the i_ino of the parent.
+ */
+struct dentry *fat_fh_to_parent(struct super_block *sb, struct fid *fid,
+                                int fh_len, int fh_type)
+{
+        return generic_fh_to_parent(sb, fid, fh_len, fh_type,
+                                    fat_nfs_get_inode);
 }
 
 /*
@@ -128,24 +89,13 @@ struct dentry *fat_get_parent(struct dentry *child_dir)
         struct super_block *sb = child_dir->d_sb;
         struct buffer_head *bh = NULL;
         struct msdos_dir_entry *de;
-        loff_t i_pos;
-        struct dentry *parent;
-        struct inode *inode;
-        int err;
+        struct inode *parent_inode = NULL;
 
-        lock_super(sb);
-
-        err = fat_get_dotdot_entry(child_dir->d_inode, &bh, &de, &i_pos);
-        if (err) {
-                parent = ERR_PTR(err);
-                goto out;
+        if (!fat_get_dotdot_entry(child_dir->d_inode, &bh, &de)) {
+                int parent_logstart = fat_get_start(MSDOS_SB(sb), de);
+                parent_inode = fat_dget(sb, parent_logstart);
         }
-        inode = fat_build_inode(sb, de, i_pos);
-
-        parent = d_obtain_alias(inode);
-out:
         brelse(bh);
-        unlock_super(sb);
 
-        return parent;
+        return d_obtain_alias(parent_inode);
 }