fs: use kmem_cache_zalloc instead

[pv_ops_mirror.git] / fs / exportfs / expfs.c

#include <linux/exportfs.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/namei.h>

#define dprintk(fmt, args...) do{}while(0)


static int get_name(struct dentry *dentry, char *name,
                struct dentry *child);


static struct dentry *exportfs_get_dentry(struct super_block *sb, void *obj)
{
        struct dentry *result = ERR_PTR(-ESTALE);

        if (sb->s_export_op->get_dentry) {
                result = sb->s_export_op->get_dentry(sb, obj);
                if (!result)
                        result = ERR_PTR(-ESTALE);
        }

        return result;
}

static int exportfs_get_name(struct dentry *dir, char *name,
                struct dentry *child)
{
        struct export_operations *nop = dir->d_sb->s_export_op;

        if (nop->get_name)
                return nop->get_name(dir, name, child);
        else
                return get_name(dir, name, child);
}

/*
 * Check if the dentry or any of it's aliases is acceptable.
 */
static struct dentry *
find_acceptable_alias(struct dentry *result,
                int (*acceptable)(void *context, struct dentry *dentry),
                void *context)
{
        struct dentry *dentry, *toput = NULL;

        if (acceptable(context, result))
                return result;

        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 root of a disconnected subtree and return a reference to it.
 */
static struct dentry *
find_disconnected_root(struct dentry *dentry)
{
        dget(dentry);
        spin_lock(&dentry->d_lock);
        while (!IS_ROOT(dentry) &&
               (dentry->d_parent->d_flags & DCACHE_DISCONNECTED)) {
                struct dentry *parent = dentry->d_parent;
                dget(parent);
                spin_unlock(&dentry->d_lock);
                dput(dentry);
                dentry = parent;
                spin_lock(&dentry->d_lock);
        }
        spin_unlock(&dentry->d_lock);
        return dentry;
}


/*
 * Make sure target_dir is fully connected to the dentry tree.
 *
 * It may already be, as the flag isn't always updated when connection happens.
 */
static int
reconnect_path(struct super_block *sb, struct dentry *target_dir)
{
        char nbuf[NAME_MAX+1];
        int noprogress = 0;
        int err = -ESTALE;

        /*
         * 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
         */
        while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
                struct dentry *pd = find_disconnected_root(target_dir);

                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.
                         *
                         * 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
                         *
                         * Getting the parent can't be supported generically,
                         * the locking is too icky.
                         *
                         * Instead we just return EACCES.  If server reboots
                         * or inodes get flushed, you lose
                         */
                        struct dentry *ppd = ERR_PTR(-EACCES);
                        struct dentry *npd;

                        mutex_lock(&pd->d_inode->i_mutex);
                        if (sb->s_export_op->get_parent)
                                ppd = sb->s_export_op->get_parent(pd);
                        mutex_unlock(&pd->d_inode->i_mutex);

                        if (IS_ERR(ppd)) {
                                err = PTR_ERR(ppd);
                                dprintk("%s: get_parent of %ld failed, err %d\n",
                                        __FUNCTION__, pd->d_inode->i_ino, err);
                                dput(pd);
                                break;
                        }

                        dprintk("%s: find name of %lu in %lu\n", __FUNCTION__,
                                pd->d_inode->i_ino, ppd->d_inode->i_ino);
                        err = exportfs_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("%s: found name: %s\n", __FUNCTION__, 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("%s: lookup failed: %d\n",
                                        __FUNCTION__, 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("%s: npd != pd\n", __FUNCTION__);
                        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;
                return err;
        }

        return 0;
}

/**
 * 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, *alias;
        int err = -ESTALE;

        /*
         * Attempt to find the inode.
         */
        result = exportfs_get_dentry(sb, obj);
        if (IS_ERR(result))
                return result;

        if (S_ISDIR(result->d_inode->i_mode)) {
                if (!(result->d_flags & DCACHE_DISCONNECTED)) {
                        if (acceptable(context, result))
                                return result;
                        err = -EACCES;
                        goto err_result;
                }

                err = reconnect_path(sb, result);
                if (err)
                        goto err_result;
        } else {
                struct dentry *target_dir, *nresult;
                char nbuf[NAME_MAX+1];

                alias = find_acceptable_alias(result, acceptable, context);
                if (alias)
                        return alias;

                if (parent == NULL)
                        goto err_result;

                target_dir = exportfs_get_dentry(sb,parent);
                if (IS_ERR(target_dir)) {
                        err = PTR_ERR(target_dir);
                        goto err_result;
                }

                err = reconnect_path(sb, target_dir);
                if (err) {
                        dput(target_dir);
                        goto err_result;
                }

                /*
                 * As we weren't after a directory, have one more step to go.
                 */
                err = exportfs_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);
        }

        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 may just be a permission problem, so returning
         * -EACCESS is safer
         */
        return ERR_PTR(-EACCES);

 err_result:
        dput(result);
        return ERR_PTR(err);
}

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;
}

/**
 * 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;
        int error;

        if (nop->encode_fh)
                error = nop->encode_fh(dentry, fh, max_len, connectable);
        else
                error = export_encode_fh(dentry, fh, max_len, connectable);

        return error;
}
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;
        struct dentry *result;

        if (nop->decode_fh) {
                result = nop->decode_fh(mnt->mnt_sb, fh, fh_len, fileid_type,
                        acceptable, context);
        } else {
                result = export_decode_fh(mnt->mnt_sb, fh, fh_len, fileid_type,
                        acceptable, context);
        }

        return result;
}
EXPORT_SYMBOL_GPL(exportfs_decode_fh);

EXPORT_SYMBOL(find_exported_dentry);

MODULE_LICENSE("GPL");