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/* 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;
}
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