expfs.c

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/*
 * Copyright (C) Neil Brown 2002
 * Copyright (C) Christoph Hellwig 2007
 *
 * This file contains the code mapping from inodes to NFS file handles,
 * and for mapping back from file handles to dentries.
 *
 * For details on why we do all the strange and hairy things in here
 * take a look at Documentation/filesystems/nfs/Exporting.
 */
#include <linux/exportfs.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/sched.h>

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


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


static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir,
        char *name, struct dentry *child)
{
    const struct export_operations *nop = dir->d_sb->s_export_op;
    struct path path = {.mnt = mnt, .dentry = dir};

    if (nop->get_name)
        return nop->get_name(dir, name, child);
    else
        return get_name(&path, 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;
    struct inode *inode;
    struct hlist_node *p;

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

    inode = result->d_inode;
    spin_lock(&inode->i_lock);
    hlist_for_each_entry(dentry, p, &inode->i_dentry, d_alias) {
        dget(dentry);
        spin_unlock(&inode->i_lock);
        if (toput)
            dput(toput);
        if (dentry != result && acceptable(context, dentry)) {
            dput(result);
            return dentry;
        }
        spin_lock(&inode->i_lock);
        toput = dentry;
    }
    spin_unlock(&inode->i_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);
    while (!IS_ROOT(dentry)) {
        struct dentry *parent = dget_parent(dentry);

        if (!(parent->d_flags & DCACHE_DISCONNECTED)) {
            dput(parent);
            break;
        }

        dput(dentry);
        dentry = parent;
    }
    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 vfsmount *mnt, struct dentry *target_dir, char *nbuf)
{
    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 == mnt->mnt_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 (mnt->mnt_sb->s_export_op->get_parent)
                ppd = mnt->mnt_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",
                    __func__, pd->d_inode->i_ino, err);
                dput(pd);
                break;
            }

            dprintk("%s: find name of %lu in %lu\n", __func__,
                pd->d_inode->i_ino, ppd->d_inode->i_ino);
            err = exportfs_get_name(mnt, 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", __func__, 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",
                    __func__, 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", __func__);
            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;
}

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;
}

static int get_name(const struct path *path, char *name, struct dentry *child)
{
    const struct cred *cred = current_cred();
    struct inode *dir = path->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(path, O_RDONLY, cred);
    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 (buffer.found) {
            error = 0;
            break;
        }

        if (error < 0)
            break;

        error = -ENOENT;
        if (old_seq == buffer.sequence)
            break;
    }

out_close:
    fput(file);
out:
    return error;
}

static int export_encode_fh(struct inode *inode, struct fid *fid,
        int *max_len, struct inode *parent)
{
    int len = *max_len;
    int type = FILEID_INO32_GEN;

    if (parent && (len < 4)) {
        *max_len = 4;
        return 255;
    } else if (len < 2) {
        *max_len = 2;
        return 255;
    }

    len = 2;
    fid->i32.ino = inode->i_ino;
    fid->i32.gen = inode->i_generation;
    if (parent) {
        fid->i32.parent_ino = parent->i_ino;
        fid->i32.parent_gen = parent->i_generation;
        len = 4;
        type = FILEID_INO32_GEN_PARENT;
    }
    *max_len = len;
    return type;
}

int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len,
        int connectable)
{
    const struct export_operations *nop = dentry->d_sb->s_export_op;
    int error;
    struct dentry *p = NULL;
    struct inode *inode = dentry->d_inode, *parent = NULL;

    if (connectable && !S_ISDIR(inode->i_mode)) {
        p = dget_parent(dentry);
        /*
         * note that while p might've ceased to be our parent already,
         * it's still pinned by and still positive.
         */
        parent = p->d_inode;
    }
    if (nop->encode_fh)
        error = nop->encode_fh(inode, fid->raw, max_len, parent);
    else
        error = export_encode_fh(inode, fid, max_len, parent);
    dput(p);

    return error;
}
EXPORT_SYMBOL_GPL(exportfs_encode_fh);

struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
        int fh_len, int fileid_type,
        int (*acceptable)(void *, struct dentry *), void *context)
{
    const struct export_operations *nop = mnt->mnt_sb->s_export_op;
    struct dentry *result, *alias;
    char nbuf[NAME_MAX+1];
    int err;

    /*
     * Try to get any dentry for the given file handle from the filesystem.
     */
    if (!nop || !nop->fh_to_dentry)
        return ERR_PTR(-ESTALE);
    result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type);
    if (!result)
        result = ERR_PTR(-ESTALE);
    if (IS_ERR(result))
        return result;

    if (S_ISDIR(result->d_inode->i_mode)) {
        /*
         * This request is for a directory.
         *
         * On the positive side there is only one dentry for each
         * directory inode.  On the negative side this implies that we
         * to ensure our dentry is connected all the way up to the
         * filesystem root.
         */
        if (result->d_flags & DCACHE_DISCONNECTED) {
            err = reconnect_path(mnt, result, nbuf);
            if (err)
                goto err_result;
        }

        if (!acceptable(context, result)) {
            err = -EACCES;
            goto err_result;
        }

        return result;
    } else {
        /*
         * It's not a directory.  Life is a little more complicated.
         */
        struct dentry *target_dir, *nresult;

        /*
         * See if either the dentry we just got from the filesystem
         * or any alias for it is acceptable.  This is always true
         * if this filesystem is exported without the subtreecheck
         * option.  If the filesystem is exported with the subtree
         * check option there's a fair chance we need to look at
         * the parent directory in the file handle and make sure
         * it's connected to the filesystem root.
         */
        alias = find_acceptable_alias(result, acceptable, context);
        if (alias)
            return alias;

        /*
         * Try to extract a dentry for the parent directory from the
         * file handle.  If this fails we'll have to give up.
         */
        err = -ESTALE;
        if (!nop->fh_to_parent)
            goto err_result;

        target_dir = nop->fh_to_parent(mnt->mnt_sb, fid,
                fh_len, fileid_type);
        if (!target_dir)
            goto err_result;
        err = PTR_ERR(target_dir);
        if (IS_ERR(target_dir))
            goto err_result;

        /*
         * And as usual we need to make sure the parent directory is
         * connected to the filesystem root.  The VFS really doesn't
         * like disconnected directories..
         */
        err = reconnect_path(mnt, target_dir, nbuf);
        if (err) {
            dput(target_dir);
            goto err_result;
        }

        /*
         * Now that we've got both a well-connected parent and a
         * dentry for the inode we're after, make sure that our
         * inode is actually connected to the parent.
         */
        err = exportfs_get_name(mnt, 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);
            }
        }

        /*
         * At this point we are done with the parent, but it's pinned
         * by the child dentry anyway.
         */
        dput(target_dir);

        /*
         * And finally make sure the dentry is actually acceptable
         * to NFSD.
         */
        alias = find_acceptable_alias(result, acceptable, context);
        if (!alias) {
            err = -EACCES;
            goto err_result;
        }

        return alias;
    }

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

MODULE_LICENSE("GPL");