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@@ -0,0 +1,151 @@
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+/* fs/fat/nfs.c
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+ *
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+ * This software is licensed under the terms of the GNU General Public
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+ * License version 2, as published by the Free Software Foundation, and
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+ * may be copied, distributed, and modified under those terms.
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+ *
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+ * This program is distributed in the hope that it will be useful,
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+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+ * GNU General Public License for more details.
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+ *
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+ */
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+
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+#include <linux/exportfs.h>
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+#include "fat.h"
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+
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+/*
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+ * a FAT file handle with fhtype 3 is
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+ * 0/ i_ino - for fast, reliable lookup if still in the cache
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+ * 1/ i_generation - to see if i_ino is still valid
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+ * bit 0 == 0 iff directory
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+ * 2/ i_pos(8-39) - if ino has changed, but still in cache
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+ * 3/ i_pos(4-7)|i_logstart - to semi-verify inode found at i_pos
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+ * 4/ i_pos(0-3)|parent->i_logstart - maybe used to hunt for the file on disc
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+ *
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+ * Hack for NFSv2: Maximum FAT entry number is 28bits and maximum
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+ * i_pos is 40bits (blocknr(32) + dir offset(8)), so two 4bits
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+ * of i_logstart is used to store the directory entry offset.
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+ */
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+
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+int
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+fat_encode_fh(struct inode *inode, __u32 *fh, int *lenp, struct inode *parent)
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+{
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+ int len = *lenp;
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+ struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
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+ loff_t i_pos;
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+
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+ if (len < 5) {
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+ *lenp = 5;
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+ return 255; /* no room */
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+ }
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+
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+ i_pos = fat_i_pos_read(sbi, inode);
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+ *lenp = 5;
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+ fh[0] = inode->i_ino;
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+ fh[1] = inode->i_generation;
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+ fh[2] = i_pos >> 8;
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+ fh[3] = ((i_pos & 0xf0) << 24) | MSDOS_I(inode)->i_logstart;
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+ fh[4] = (i_pos & 0x0f) << 28;
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+ if (parent)
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+ fh[4] |= MSDOS_I(parent)->i_logstart;
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+ return 3;
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+}
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+
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+static int fat_is_valid_fh(int fh_len, int fh_type)
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+{
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+ return ((fh_len >= 5) && (fh_type == 3));
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+}
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+
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+/**
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+ * Map a NFS file handle to a corresponding dentry.
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+ * The dentry may or may not be connected to the filesystem root.
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+ */
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+struct dentry *fat_fh_to_dentry(struct super_block *sb, struct fid *fid,
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+ int fh_len, int fh_type)
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+{
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+ struct inode *inode = NULL;
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+ u32 *fh = fid->raw;
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+ loff_t i_pos;
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+ unsigned long i_ino;
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+ __u32 i_generation;
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+ int i_logstart;
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+
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+ if (!fat_is_valid_fh(fh_len, fh_type))
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+ return NULL;
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+
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+ i_ino = fh[0];
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+ i_generation = fh[1];
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+ i_logstart = fh[3] & 0x0fffffff;
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+
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+ /* Try i_ino lookup first - fastest and most reliable */
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+ inode = ilookup(sb, i_ino);
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+ if (inode && (inode->i_generation != i_generation)) {
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+ iput(inode);
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+ inode = NULL;
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+ }
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+ if (!inode) {
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+ i_pos = (loff_t)fh[2] << 8;
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+ i_pos |= ((fh[3] >> 24) & 0xf0) | (fh[4] >> 28);
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+
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+ /* try 2 - see if i_pos is in F-d-c
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+ * require i_logstart to be the same
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+ * Will fail if you truncate and then re-write
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+ */
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+
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+ inode = fat_iget(sb, i_pos);
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+ if (inode && MSDOS_I(inode)->i_logstart != i_logstart) {
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+ iput(inode);
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+ inode = NULL;
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+ }
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+ }
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+
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+ /*
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+ * For now, do nothing if the inode is not found.
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+ *
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+ * What we could do is:
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+ *
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+ * - follow the file starting at fh[4], and record the ".." entry,
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+ * and the name of the fh[2] entry.
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+ * - then follow the ".." file finding the next step up.
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+ *
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+ * This way we build a path to the root of the tree. If this works, we
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+ * lookup the path and so get this inode into the cache. Finally try
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+ * the fat_iget lookup again. If that fails, then we are totally out
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+ * of luck. But all that is for another day
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+ */
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+ return d_obtain_alias(inode);
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+}
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+
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+/*
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+ * Find the parent for a directory that is not currently connected to
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+ * the filesystem root.
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+ *
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+ * On entry, the caller holds child_dir->d_inode->i_mutex.
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+ */
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+struct dentry *fat_get_parent(struct dentry *child_dir)
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+{
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+ struct super_block *sb = child_dir->d_sb;
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+ struct buffer_head *bh = NULL;
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+ struct msdos_dir_entry *de;
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+ loff_t i_pos;
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+ struct dentry *parent;
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+ struct inode *inode;
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+ int err;
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+
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+ lock_super(sb);
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+
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+ err = fat_get_dotdot_entry(child_dir->d_inode, &bh, &de, &i_pos);
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+ if (err) {
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+ parent = ERR_PTR(err);
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+ goto out;
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+ }
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+ inode = fat_build_inode(sb, de, i_pos);
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+
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+ parent = d_obtain_alias(inode);
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+out:
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+ brelse(bh);
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+ unlock_super(sb);
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+
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+ return parent;
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+}
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Steven J. Magnani