498 lines
12 KiB
C
498 lines
12 KiB
C
/*
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* Copyright (C) Neil Brown 2002
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* Copyright (C) Christoph Hellwig 2007
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*
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* This file contains the code mapping from inodes to NFS file handles,
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* and for mapping back from file handles to dentries.
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*
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* For details on why we do all the strange and hairy things in here
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* take a look at Documentation/filesystems/nfs/Exporting.
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*/
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#include <linux/exportfs.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include <linux/module.h>
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#include <linux/mount.h>
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#include <linux/namei.h>
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#include <linux/sched.h>
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#define dprintk(fmt, args...) do{}while(0)
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static int get_name(struct vfsmount *mnt, struct dentry *dentry, char *name,
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struct dentry *child);
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static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
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char *name, struct dentry *child)
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{
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const struct export_operations *nop = dir->d_sb->s_export_op;
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if (nop->get_name)
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return nop->get_name(dir, name, child);
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else
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return get_name(mnt, dir, name, child);
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}
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/*
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* Check if the dentry or any of it's aliases is acceptable.
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*/
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static struct dentry *
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find_acceptable_alias(struct dentry *result,
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int (*acceptable)(void *context, struct dentry *dentry),
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void *context)
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{
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struct dentry *dentry, *toput = NULL;
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struct inode *inode;
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if (acceptable(context, result))
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return result;
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inode = result->d_inode;
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spin_lock(&inode->i_lock);
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list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
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dget(dentry);
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spin_unlock(&inode->i_lock);
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if (toput)
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dput(toput);
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if (dentry != result && acceptable(context, dentry)) {
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dput(result);
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return dentry;
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}
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spin_lock(&inode->i_lock);
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toput = dentry;
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}
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spin_unlock(&inode->i_lock);
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if (toput)
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dput(toput);
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return NULL;
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}
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/*
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* Find root of a disconnected subtree and return a reference to it.
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*/
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static struct dentry *
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find_disconnected_root(struct dentry *dentry)
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{
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dget(dentry);
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while (!IS_ROOT(dentry)) {
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struct dentry *parent = dget_parent(dentry);
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if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
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dput(parent);
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break;
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}
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dput(dentry);
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dentry = parent;
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}
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return dentry;
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}
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/*
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* Make sure target_dir is fully connected to the dentry tree.
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*
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* It may already be, as the flag isn't always updated when connection happens.
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*/
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static int
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reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf)
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{
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int noprogress = 0;
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int err = -ESTALE;
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/*
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* It is possible that a confused file system might not let us complete
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* the path to the root. For example, if get_parent returns a directory
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* in which we cannot find a name for the child. While this implies a
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* very sick filesystem we don't want it to cause knfsd to spin. Hence
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* the noprogress counter. If we go through the loop 10 times (2 is
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* probably enough) without getting anywhere, we just give up
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*/
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while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
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struct dentry *pd = find_disconnected_root(target_dir);
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if (!IS_ROOT(pd)) {
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/* must have found a connected parent - great */
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spin_lock(&pd->d_lock);
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pd->d_flags &= ~DCACHE_DISCONNECTED;
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spin_unlock(&pd->d_lock);
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noprogress = 0;
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} else if (pd == mnt->mnt_sb->s_root) {
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printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
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spin_lock(&pd->d_lock);
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pd->d_flags &= ~DCACHE_DISCONNECTED;
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spin_unlock(&pd->d_lock);
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noprogress = 0;
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} else {
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/*
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* We have hit the top of a disconnected path, try to
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* find parent and connect.
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*
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* Racing with some other process renaming a directory
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* isn't much of a problem here. If someone renames
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* the directory, it will end up properly connected,
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* which is what we want
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*
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* Getting the parent can't be supported generically,
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* the locking is too icky.
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*
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* Instead we just return EACCES. If server reboots
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* or inodes get flushed, you lose
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*/
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struct dentry *ppd = ERR_PTR(-EACCES);
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struct dentry *npd;
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mutex_lock(&pd->d_inode->i_mutex);
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if (mnt->mnt_sb->s_export_op->get_parent)
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ppd = mnt->mnt_sb->s_export_op->get_parent(pd);
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mutex_unlock(&pd->d_inode->i_mutex);
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if (IS_ERR(ppd)) {
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err = PTR_ERR(ppd);
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dprintk("%s: get_parent of %ld failed, err %d\n",
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__func__, pd->d_inode->i_ino, err);
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dput(pd);
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break;
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}
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dprintk("%s: find name of %lu in %lu\n", __func__,
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pd->d_inode->i_ino, ppd->d_inode->i_ino);
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err = exportfs_get_name(mnt, ppd, nbuf, pd);
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if (err) {
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dput(ppd);
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dput(pd);
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if (err == -ENOENT)
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/* some race between get_parent and
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* get_name? just try again
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*/
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continue;
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break;
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}
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dprintk("%s: found name: %s\n", __func__, nbuf);
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mutex_lock(&ppd->d_inode->i_mutex);
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npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
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mutex_unlock(&ppd->d_inode->i_mutex);
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if (IS_ERR(npd)) {
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err = PTR_ERR(npd);
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dprintk("%s: lookup failed: %d\n",
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__func__, err);
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dput(ppd);
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dput(pd);
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break;
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}
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/* we didn't really want npd, we really wanted
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* a side-effect of the lookup.
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* hopefully, npd == pd, though it isn't really
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* a problem if it isn't
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*/
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if (npd == pd)
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noprogress = 0;
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else
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printk("%s: npd != pd\n", __func__);
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dput(npd);
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dput(ppd);
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if (IS_ROOT(pd)) {
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/* something went wrong, we have to give up */
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dput(pd);
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break;
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}
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}
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dput(pd);
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}
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if (target_dir->d_flags & DCACHE_DISCONNECTED) {
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/* something went wrong - oh-well */
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if (!err)
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err = -ESTALE;
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return err;
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}
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return 0;
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}
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struct getdents_callback {
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char *name; /* name that was found. It already points to a
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buffer NAME_MAX+1 is size */
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unsigned long ino; /* the inum we are looking for */
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int found; /* inode matched? */
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int sequence; /* sequence counter */
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};
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/*
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* A rather strange filldir function to capture
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* the name matching the specified inode number.
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*/
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static int filldir_one(void * __buf, const char * name, int len,
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loff_t pos, u64 ino, unsigned int d_type)
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{
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struct getdents_callback *buf = __buf;
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int result = 0;
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buf->sequence++;
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if (buf->ino == ino) {
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memcpy(buf->name, name, len);
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buf->name[len] = '\0';
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buf->found = 1;
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result = -1;
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}
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return result;
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}
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/**
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* get_name - default export_operations->get_name function
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* @dentry: the directory in which to find a name
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* @name: a pointer to a %NAME_MAX+1 char buffer to store the name
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* @child: the dentry for the child directory.
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*
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* calls readdir on the parent until it finds an entry with
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* the same inode number as the child, and returns that.
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*/
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static int get_name(struct vfsmount *mnt, struct dentry *dentry,
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char *name, struct dentry *child)
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{
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const struct cred *cred = current_cred();
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struct inode *dir = dentry->d_inode;
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int error;
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struct file *file;
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struct getdents_callback buffer;
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error = -ENOTDIR;
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if (!dir || !S_ISDIR(dir->i_mode))
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goto out;
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error = -EINVAL;
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if (!dir->i_fop)
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goto out;
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/*
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* Open the directory ...
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*/
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file = dentry_open(dget(dentry), mntget(mnt), O_RDONLY, cred);
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error = PTR_ERR(file);
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if (IS_ERR(file))
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goto out;
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error = -EINVAL;
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if (!file->f_op->readdir)
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goto out_close;
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buffer.name = name;
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buffer.ino = child->d_inode->i_ino;
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buffer.found = 0;
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buffer.sequence = 0;
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while (1) {
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int old_seq = buffer.sequence;
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error = vfs_readdir(file, filldir_one, &buffer);
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if (buffer.found) {
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error = 0;
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break;
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}
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if (error < 0)
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break;
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error = -ENOENT;
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if (old_seq == buffer.sequence)
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break;
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}
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out_close:
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fput(file);
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out:
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return error;
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}
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/**
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* export_encode_fh - default export_operations->encode_fh function
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* @dentry: the dentry to encode
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* @fh: where to store the file handle fragment
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* @max_len: maximum length to store there
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* @connectable: whether to store parent information
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*
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* This default encode_fh function assumes that the 32 inode number
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* is suitable for locating an inode, and that the generation number
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* can be used to check that it is still valid. It places them in the
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* filehandle fragment where export_decode_fh expects to find them.
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*/
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static int export_encode_fh(struct dentry *dentry, struct fid *fid,
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int *max_len, int connectable)
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{
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struct inode * inode = dentry->d_inode;
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int len = *max_len;
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int type = FILEID_INO32_GEN;
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if (connectable && (len < 4)) {
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*max_len = 4;
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return 255;
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} else if (len < 2) {
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*max_len = 2;
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return 255;
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}
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len = 2;
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fid->i32.ino = inode->i_ino;
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fid->i32.gen = inode->i_generation;
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if (connectable && !S_ISDIR(inode->i_mode)) {
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struct inode *parent;
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spin_lock(&dentry->d_lock);
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parent = dentry->d_parent->d_inode;
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fid->i32.parent_ino = parent->i_ino;
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fid->i32.parent_gen = parent->i_generation;
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spin_unlock(&dentry->d_lock);
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len = 4;
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type = FILEID_INO32_GEN_PARENT;
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}
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*max_len = len;
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return type;
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}
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int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
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int connectable)
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{
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const struct export_operations *nop = dentry->d_sb->s_export_op;
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int error;
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if (nop->encode_fh)
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error = nop->encode_fh(dentry, fid->raw, max_len, connectable);
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else
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error = export_encode_fh(dentry, fid, max_len, connectable);
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return error;
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}
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EXPORT_SYMBOL_GPL(exportfs_encode_fh);
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struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
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int fh_len, int fileid_type,
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int (*acceptable)(void *, struct dentry *), void *context)
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{
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const struct export_operations *nop = mnt->mnt_sb->s_export_op;
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struct dentry *result, *alias;
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char nbuf[NAME_MAX+1];
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int err;
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/*
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* Try to get any dentry for the given file handle from the filesystem.
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*/
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if (!nop || !nop->fh_to_dentry)
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return ERR_PTR(-ESTALE);
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result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
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if (!result)
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result = ERR_PTR(-ESTALE);
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if (IS_ERR(result))
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return result;
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if (S_ISDIR(result->d_inode->i_mode)) {
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/*
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* This request is for a directory.
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*
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* On the positive side there is only one dentry for each
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* directory inode. On the negative side this implies that we
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* to ensure our dentry is connected all the way up to the
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* filesystem root.
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*/
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if (result->d_flags & DCACHE_DISCONNECTED) {
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err = reconnect_path(mnt, result, nbuf);
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if (err)
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goto err_result;
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}
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if (!acceptable(context, result)) {
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err = -EACCES;
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goto err_result;
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}
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return result;
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} else {
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/*
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* It's not a directory. Life is a little more complicated.
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*/
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struct dentry *target_dir, *nresult;
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/*
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* See if either the dentry we just got from the filesystem
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* or any alias for it is acceptable. This is always true
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* if this filesystem is exported without the subtreecheck
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* option. If the filesystem is exported with the subtree
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* check option there's a fair chance we need to look at
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* the parent directory in the file handle and make sure
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* it's connected to the filesystem root.
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*/
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alias = find_acceptable_alias(result, acceptable, context);
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if (alias)
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return alias;
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/*
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* Try to extract a dentry for the parent directory from the
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* file handle. If this fails we'll have to give up.
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*/
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err = -ESTALE;
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if (!nop->fh_to_parent)
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goto err_result;
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target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
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fh_len, fileid_type);
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if (!target_dir)
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goto err_result;
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err = PTR_ERR(target_dir);
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if (IS_ERR(target_dir))
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goto err_result;
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/*
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* And as usual we need to make sure the parent directory is
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* connected to the filesystem root. The VFS really doesn't
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* like disconnected directories..
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*/
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err = reconnect_path(mnt, target_dir, nbuf);
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if (err) {
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dput(target_dir);
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goto err_result;
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}
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/*
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* Now that we've got both a well-connected parent and a
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* dentry for the inode we're after, make sure that our
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* inode is actually connected to the parent.
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*/
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err = exportfs_get_name(mnt, target_dir, nbuf, result);
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if (!err) {
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mutex_lock(&target_dir->d_inode->i_mutex);
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nresult = lookup_one_len(nbuf, target_dir,
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strlen(nbuf));
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mutex_unlock(&target_dir->d_inode->i_mutex);
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if (!IS_ERR(nresult)) {
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if (nresult->d_inode) {
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dput(result);
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result = nresult;
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} else
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dput(nresult);
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}
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}
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/*
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* At this point we are done with the parent, but it's pinned
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* by the child dentry anyway.
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*/
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dput(target_dir);
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/*
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* And finally make sure the dentry is actually acceptable
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* to NFSD.
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*/
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alias = find_acceptable_alias(result, acceptable, context);
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if (!alias) {
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err = -EACCES;
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goto err_result;
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}
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return alias;
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}
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err_result:
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dput(result);
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return ERR_PTR(err);
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}
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EXPORT_SYMBOL_GPL(exportfs_decode_fh);
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MODULE_LICENSE("GPL");
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