#include <linux/exportfs.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/namei.h>
struct export_operations export_op_default;
#define CALL(ops,fun) ((ops->fun)?(ops->fun):export_op_default.fun)
#define dprintk(fmt, args...) do{}while(0)
static struct dentry *
find_acceptable_alias(struct dentry *result,
int (*acceptable)(void *context, struct dentry *dentry),
void *context)
{
struct dentry *dentry, *toput = NULL;
spin_lock(&dcache_lock);
list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) {
dget_locked(dentry);
spin_unlock(&dcache_lock);
if (toput)
dput(toput);
if (dentry != result && acceptable(context, dentry)) {
dput(result);
return dentry;
}
spin_lock(&dcache_lock);
toput = dentry;
}
spin_unlock(&dcache_lock);
if (toput)
dput(toput);
return NULL;
}
/**
* find_exported_dentry - helper routine to implement export_operations->decode_fh
* @sb: The &super_block identifying the filesystem
* @obj: An opaque identifier of the object to be found - passed to
* get_inode
* @parent: An optional opqaue identifier of the parent of the object.
* @acceptable: A function used to test possible &dentries to see if they are
* acceptable
* @context: A parameter to @acceptable so that it knows on what basis to
* judge.
*
* find_exported_dentry is the central helper routine to enable file systems
* to provide the decode_fh() export_operation. It's main task is to take
* an &inode, find or create an appropriate &dentry structure, and possibly
* splice this into the dcache in the correct place.
*
* The decode_fh() operation provided by the filesystem should call
* find_exported_dentry() with the same parameters that it received except
* that instead of the file handle fragment, pointers to opaque identifiers
* for the object and optionally its parent are passed. The default decode_fh
* routine passes one pointer to the start of the filehandle fragment, and
* one 8 bytes into the fragment. It is expected that most filesystems will
* take this approach, though the offset to the parent identifier may well be
* different.
*
* find_exported_dentry() will call get_dentry to get an dentry pointer from
* the file system. If any &dentry in the d_alias list is acceptable, it will
* be returned. Otherwise find_exported_dentry() will attempt to splice a new
* &dentry into the dcache using get_name() and get_parent() to find the
* appropriate place.
*/
struct dentry *
find_exported_dentry(struct super_block *sb, void *obj, void *parent,
int (*acceptable)(void *context, struct dentry *de),
void *context)
{
struct dentry *result = NULL;
struct dentry *target_dir;
int err;
struct export_operations *nops = sb->s_export_op;
struct dentry *alias;
int noprogress;
char nbuf[NAME_MAX+1];
/*
* Attempt to find the inode.
*/
result = CALL(sb->s_export_op,get_dentry)(sb,obj);
err = -ESTALE;
if (result == NULL)
goto err_out;
if (IS_ERR(result)) {
err = PTR_ERR(result);
goto err_out;
}
if (S_ISDIR(result->d_inode->i_mode) &&
(result->d_flags & DCACHE_DISCONNECTED)) {
/* it is an unconnected directory, we must connect it */
;
} else {
if (acceptable(context, result))
return result;
if (S_ISDIR(result->d_inode->i_mode)) {
err = -EACCES;
goto err_result;
}
alias = find_acceptable_alias(result, acceptable, context);
if (alias)
return alias;
}
/* It's a directory, or we are required to confirm the file's
* location in the tree based on the parent information
*/
dprintk("find_exported_dentry: need to look harder for %s/%d\n",sb->s_id,*(int*)obj);
if (S_ISDIR(result->d_inode->i_mode))
target_dir = dget(result);
else {
if (parent == NULL)
goto err_result;
target_dir = CALL(sb->s_export_op,get_dentry)(sb,parent);
if (IS_ERR(target_dir))
err = PTR_ERR(target_dir);
if (target_dir == NULL || IS_ERR(target_dir))
goto err_result;
}
/*
* Now we need to make sure that target_dir is properly connected.
* It may already be, as the flag isn't always updated when connection
* happens.
* So, we walk up parent links until we find a connected directory,
* or we run out of directories. Then we find the parent, find
* the name of the child in that parent, and do a lookup.
* This should connect the child into the parent
* We then repeat.
*/
/* it is possible that a confused file system might not let us complete
* the path to the root. For example, if get_parent returns a directory
* in which we cannot find a name for the child. While this implies a
* very sick filesystem we don't want it to cause knfsd to spin. Hence
* the noprogress counter. If we go through the loop 10 times (2 is
* probably enough) without getting anywhere, we just give up
*/
noprogress= 0;
while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
struct dentry *pd = target_dir;
dget(pd);
spin_lock(&pd->d_lock);
while (!IS_ROOT(pd) &&
(pd->d_parent->d_flags&DCACHE_DISCONNECTED)) {
struct dentry *parent = pd->d_parent;
dget(parent);
spin_unlock(&pd->d_lock);
dput(pd);
pd = parent;
spin_lock(&pd->d_lock);
}
spin_unlock(&pd->d_lock);
if (!IS_ROOT(pd)) {
/* must have found a connected parent - great */
spin_lock(&pd->d_lock);
pd->d_flags &= ~DCACHE_DISCONNECTED;
spin_unlock(&pd->d_lock);
noprogress = 0;
} else if (pd == sb->s_root) {
printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
spin_lock(&pd->d_lock);
pd->d_flags &= ~DCACHE_DISCONNECTED;
spin_unlock(&pd->d_lock);
noprogress = 0;
} else {
/* we have hit the top of a disconnected path. Try
* to find parent and connect
* note: racing with some other process renaming a
* directory isn't much of a problem here. If someone
* renames the directory, it will end up properly
* connected, which is what we want
*/
struct dentry *ppd;
struct dentry *npd;
mutex_lock(&pd->d_inode->i_mutex);
ppd = CALL(nops,get_parent)(pd);
mutex_unlock(&pd->d_inode->i_mutex);
if (IS_ERR(ppd)) {
err = PTR_ERR(ppd);
dprintk("find_exported_dentry: get_parent of %ld failed, err %d\n",
pd->d_inode->i_ino, err);
dput(pd);
break;
}
dprintk("find_exported_dentry: find name of %lu in %lu\n", pd->d_inode->i_ino, ppd->d_inode->i_ino);
err = CALL(nops,get_name)(ppd, nbuf, pd);
if (err) {
dput(ppd);
dput(pd);
if (err == -ENOENT)
/* some race between get_parent and
* get_name? just try again
*/
continue;
break;
}
dprintk("find_exported_dentry: found name: %s\n", nbuf);
mutex_lock(&ppd->d_inode->i_mutex);
npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
mutex_unlock(&ppd->d_inode->i_mutex);
if (IS_ERR(npd)) {
err = PTR_ERR(npd);
dprintk("find_exported_dentry: lookup failed: %d\n", err);
dput(ppd);
dput(pd);
break;
}
/* we didn't really want npd, we really wanted
* a side-effect of the lookup.
* hopefully, npd == pd, though it isn't really
* a problem if it isn't
*/
if (npd == pd)
noprogress = 0;
else
printk("find_exported_dentry: npd != pd\n");
dput(npd);
dput(ppd);
if (IS_ROOT(pd)) {
/* something went wrong, we have to give up */
dput(pd);
break;
}
}
dput(pd);
}
if (target_dir->d_flags & DCACHE_DISCONNECTED) {
/* something went wrong - oh-well */
if (!err)
err = -ESTALE;
goto err_target;
}
/* if we weren't after a directory, have one more step to go */
if (result != target_dir) {
struct dentry *nresult;
err = CALL(nops,get_name)(target_dir, nbuf, result);
if (!err) {
mutex_lock(&target_dir->d_inode->i_mutex);
nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
mutex_unlock(&target_dir->d_inode->i_mutex);
if (!IS_ERR(nresult)) {
if (nresult->d_inode) {
dput(result);
result = nresult;
} else
dput(nresult);
}
}
}
dput(target_dir);
/* now result is properly connected, it is our best bet */
if (acceptable(context, result))
return result;
alias = find_acceptable_alias(result, acceptable, context);
if (alias)
return alias;
/* drat - I just cannot find anything acceptable */
dput(result);
/* It might be justifiable to return ESTALE here,
* but the filehandle at-least looks reasonable good
* and it just be a permission problem, so returning
* -EACCESS is safer
*/
return ERR_PTR(-EACCES);
err_target:
dput(target_dir);
err_result:
dput(result);
err_out:
return ERR_PTR(err);
}
static struct dentry *get_parent(struct dentry *child)
{
/* get_parent cannot be supported generically, the locking
* is too icky.
* instead, we just return EACCES. If server reboots or inodes
* get flushed, you lose
*/
return ERR_PTR(-EACCES);
}
struct getdents_callback {
char *name; /* name that was found. It already points to a
buffer NAME_MAX+1 is size */
unsigned long ino; /* the inum we are looking for */
int found; /* inode matched? */
int sequence; /* sequence counter */
};
/*
* A rather strange filldir function to capture
* the name matching the specified inode number.
*/
static int filldir_one(void * __buf, const char * name, int len,
loff_t pos, u64 ino, unsigned int d_type)
{
struct getdents_callback *buf = __buf;
int result = 0;
buf->sequence++;
if (buf->ino == ino) {
memcpy(buf->name, name, len);
buf->name[len] = '\0';
buf->found = 1;
result = -1;
}
return result;
}
/**
* get_name - default export_operations->get_name function
* @dentry: the directory in which to find a name
* @name: a pointer to a %NAME_MAX+1 char buffer to store the name
* @child: the dentry for the child directory.
*
* calls readdir on the parent until it finds an entry with
* the same inode number as the child, and returns that.
*/
static int get_name(struct dentry *dentry, char *name,
struct dentry *child)
{
struct inode *dir = dentry->d_inode;
int error;
struct file *file;
struct getdents_callback buffer;
error = -ENOTDIR;
if (!dir || !S_ISDIR(dir->i_mode))
goto out;
error = -EINVAL;
if (!dir->i_fop)
goto out;
/*
* Open the directory ...
*/
file = dentry_open(dget(dentry), NULL, O_RDONLY);
error = PTR_ERR(file);
if (IS_ERR(file))
goto out;
error = -EINVAL;
if (!file->f_op->readdir)
goto out_close;
buffer.name = name;
buffer.ino = child->d_inode->i_ino;
buffer.found = 0;
buffer.sequence = 0;
while (1) {
int old_seq = buffer.sequence;
error = vfs_readdir(file, filldir_one, &buffer);
if (error < 0)
break;
error = 0;
if (buffer.found)
break;
error = -ENOENT;
if (old_seq == buffer.sequence)
break;
}
out_close:
fput(file);
out:
return error;
}
static struct dentry *get_dentry(struct super_block *sb, void *vobjp)
{
return ERR_PTR(-ESTALE);
}
/**
* export_encode_fh - default export_operations->encode_fh function
* @dentry: the dentry to encode
* @fh: where to store the file handle fragment
* @max_len: maximum length to store there
* @connectable: whether to store parent information
*
* This default encode_fh function assumes that the 32 inode number
* is suitable for locating an inode, and that the generation number
* can be used to check that it is still valid. It places them in the
* filehandle fragment where export_decode_fh expects to find them.
*/
static int export_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
int connectable)
{
struct inode * inode = dentry->d_inode;
int len = *max_len;
int type = 1;
if (len < 2 || (connectable && len < 4))
return 255;
len = 2;
fh[0] = inode->i_ino;
fh[1] = inode->i_generation;
if (connectable && !S_ISDIR(inode->i_mode)) {
struct inode *parent;
spin_lock(&dentry->d_lock);
parent = dentry->d_parent->d_inode;
fh[2] = parent->i_ino;
fh[3] = parent->i_generation;
spin_unlock(&dentry->d_lock);
len = 4;
type = 2;
}
*max_len = len;
return type;
}
/**
* export_decode_fh - default export_operations->decode_fh function
* @sb: The superblock
* @fh: pointer to the file handle fragment
* @fh_len: length of file handle fragment
* @acceptable: function for testing acceptability of dentrys
* @context: context for @acceptable
*
* This is the default decode_fh() function.
* a fileid_type of 1 indicates that the filehandlefragment
* just contains an object identifier understood by get_dentry.
* a fileid_type of 2 says that there is also a directory
* identifier 8 bytes in to the filehandlefragement.
*/
static struct dentry *export_decode_fh(struct super_block *sb, __u32 *fh, int fh_len,
int fileid_type,
int (*acceptable)(void *context, struct dentry *de),
void *context)
{
__u32 parent[2];
parent[0] = parent[1] = 0;
if (fh_len < 2 || fileid_type > 2)
return NULL;
if (fileid_type == 2) {
if (fh_len > 2) parent[0] = fh[2];
if (fh_len > 3) parent[1] = fh[3];
}
return find_exported_dentry(sb, fh, parent,
acceptable, context);
}
int exportfs_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
int connectable)
{
struct export_operations *nop = dentry->d_sb->s_export_op;
return CALL(nop, encode_fh)(dentry, fh, max_len, connectable);
}
EXPORT_SYMBOL_GPL(exportfs_encode_fh);
struct dentry *exportfs_decode_fh(struct vfsmount *mnt, __u32 *fh, int fh_len,
int fileid_type, int (*acceptable)(void *, struct dentry *),
void *context)
{
struct export_operations *nop = mnt->mnt_sb->s_export_op;
return CALL(nop, decode_fh)(mnt->mnt_sb, fh, fh_len, fileid_type,
acceptable, context);
}
EXPORT_SYMBOL_GPL(exportfs_decode_fh);
struct export_operations export_op_default = {
.decode_fh = export_decode_fh,
.encode_fh = export_encode_fh,
.get_name = get_name,
.get_parent = get_parent,
.get_dentry = get_dentry,
};
EXPORT_SYMBOL(find_exported_dentry);
MODULE_LICENSE("GPL");
