1 files changed, 151 insertions, 0 deletions
diff --git a/fs/fat/nfs.c b/fs/fat/nfs.c
new file mode 100644
index 000000000000..21609a1e9355
--- /dev/null
+++ b/fs/fat/nfs.c
@@ -0,0 +1,151 @@
+/* fs/fat/nfs.c
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#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.
+ */
+
+int
+fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp, struct inode *parent)
+{
+	int len = *lenp;
+	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
+	loff_t i_pos;
+
+	if (len < 5) {
+		*lenp = 5;
+		return 255; /* no room */
+	}
+
+	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;
+}
+
+static int fat_is_valid_fh(int fh_len, int fh_type)
+{
+	return ((fh_len >= 5) && (fh_type == 3));
+}
+
+/**
+ * Map a NFS file handle to a corresponding dentry.
+ * The dentry may or may not be connected to the filesystem root.
+ */
+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;
+		}
+	}
+
+	/*
+	 * 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 directory that is not currently connected to
+ * the filesystem root.
+ *
+ * On entry, the caller holds child_dir->d_inode->i_mutex.
+ */
+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;
+
+	lock_super(sb);
+
+	err = fat_get_dotdot_entry(child_dir->d_inode, &bh, &de, &i_pos);
+	if (err) {
+		parent = ERR_PTR(err);
+		goto out;
+	}
+	inode = fat_build_inode(sb, de, i_pos);
+
+	parent = d_obtain_alias(inode);
+out:
+	brelse(bh);
+	unlock_super(sb);
+
+	return parent;
+}