fid.c

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/*
 * V9FS FID Management
 *
 *  Copyright (C) 2007 by Latchesar Ionkov <[email protected]>
 *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  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.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to:
 *  Free Software Foundation
 *  51 Franklin Street, Fifth Floor
 *  Boston, MA  02111-1301  USA
 *
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/idr.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>

#include "v9fs.h"
#include "v9fs_vfs.h"
#include "fid.h"

int v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
{
    struct v9fs_dentry *dent;

    p9_debug(P9_DEBUG_VFS, "fid %d dentry %s\n",
         fid->fid, dentry->d_name.name);

    dent = dentry->d_fsdata;
    if (!dent) {
        dent = kmalloc(sizeof(struct v9fs_dentry), GFP_KERNEL);
        if (!dent)
            return -ENOMEM;

        spin_lock_init(&dent->lock);
        INIT_LIST_HEAD(&dent->fidlist);
        dentry->d_fsdata = dent;
    }

    spin_lock(&dent->lock);
    list_add(&fid->dlist, &dent->fidlist);
    spin_unlock(&dent->lock);

    return 0;
}

static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)
{
    struct v9fs_dentry *dent;
    struct p9_fid *fid, *ret;

    p9_debug(P9_DEBUG_VFS, " dentry: %s (%p) uid %d any %d\n",
         dentry->d_name.name, dentry, uid, any);
    dent = (struct v9fs_dentry *) dentry->d_fsdata;
    ret = NULL;
    if (dent) {
        spin_lock(&dent->lock);
        list_for_each_entry(fid, &dent->fidlist, dlist) {
            if (any || fid->uid == uid) {
                ret = fid;
                break;
            }
        }
        spin_unlock(&dent->lock);
    }

    return ret;
}

/*
 * We need to hold v9ses->rename_sem as long as we hold references
 * to returned path array. Array element contain pointers to
 * dentry names.
 */
static int build_path_from_dentry(struct v9fs_session_info *v9ses,
                  struct dentry *dentry, char ***names)
{
    int n = 0, i;
    char **wnames;
    struct dentry *ds;

    for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
        n++;

    wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
    if (!wnames)
        goto err_out;

    for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
        wnames[i] = (char  *)ds->d_name.name;

    *names = wnames;
    return n;
err_out:
    return -ENOMEM;
}

static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
                           uid_t uid, int any)
{
    struct dentry *ds;
    char **wnames, *uname;
    int i, n, l, clone, access;
    struct v9fs_session_info *v9ses;
    struct p9_fid *fid, *old_fid = NULL;

    v9ses = v9fs_dentry2v9ses(dentry);
    access = v9ses->flags & V9FS_ACCESS_MASK;
    fid = v9fs_fid_find(dentry, uid, any);
    if (fid)
        return fid;
    /*
     * we don't have a matching fid. To do a TWALK we need
     * parent fid. We need to prevent rename when we want to
     * look at the parent.
     */
    down_read(&v9ses->rename_sem);
    ds = dentry->d_parent;
    fid = v9fs_fid_find(ds, uid, any);
    if (fid) {
        /* Found the parent fid do a lookup with that */
        fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
        goto fid_out;
    }
    up_read(&v9ses->rename_sem);

    /* start from the root and try to do a lookup */
    fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
    if (!fid) {
        /* the user is not attached to the fs yet */
        if (access == V9FS_ACCESS_SINGLE)
            return ERR_PTR(-EPERM);

        if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
                uname = NULL;
        else
            uname = v9ses->uname;

        fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
                       v9ses->aname);
        if (IS_ERR(fid))
            return fid;

        v9fs_fid_add(dentry->d_sb->s_root, fid);
    }
    /* If we are root ourself just return that */
    if (dentry->d_sb->s_root == dentry)
        return fid;
    /*
     * Do a multipath walk with attached root.
     * When walking parent we need to make sure we
     * don't have a parallel rename happening
     */
    down_read(&v9ses->rename_sem);
    n  = build_path_from_dentry(v9ses, dentry, &wnames);
    if (n < 0) {
        fid = ERR_PTR(n);
        goto err_out;
    }
    clone = 1;
    i = 0;
    while (i < n) {
        l = min(n - i, P9_MAXWELEM);
        /*
         * We need to hold rename lock when doing a multipath
         * walk to ensure none of the patch component change
         */
        fid = p9_client_walk(fid, l, &wnames[i], clone);
        if (IS_ERR(fid)) {
            if (old_fid) {
                /*
                 * If we fail, clunk fid which are mapping
                 * to path component and not the last component
                 * of the path.
                 */
                p9_client_clunk(old_fid);
            }
            kfree(wnames);
            goto err_out;
        }
        old_fid = fid;
        i += l;
        clone = 0;
    }
    kfree(wnames);
fid_out:
    if (!IS_ERR(fid))
        v9fs_fid_add(dentry, fid);
err_out:
    up_read(&v9ses->rename_sem);
    return fid;
}

struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
{
    uid_t uid;
    int  any, access;
    struct v9fs_session_info *v9ses;

    v9ses = v9fs_dentry2v9ses(dentry);
    access = v9ses->flags & V9FS_ACCESS_MASK;
    switch (access) {
    case V9FS_ACCESS_SINGLE:
    case V9FS_ACCESS_USER:
    case V9FS_ACCESS_CLIENT:
        uid = current_fsuid();
        any = 0;
        break;

    case V9FS_ACCESS_ANY:
        uid = v9ses->uid;
        any = 1;
        break;

    default:
        uid = ~0;
        any = 0;
        break;
    }
    return v9fs_fid_lookup_with_uid(dentry, uid, any);
}

struct p9_fid *v9fs_fid_clone(struct dentry *dentry)
{
    struct p9_fid *fid, *ret;

    fid = v9fs_fid_lookup(dentry);
    if (IS_ERR(fid))
        return fid;

    ret = p9_client_walk(fid, 0, NULL, 1);
    return ret;
}

static struct p9_fid *v9fs_fid_clone_with_uid(struct dentry *dentry, uid_t uid)
{
    struct p9_fid *fid, *ret;

    fid = v9fs_fid_lookup_with_uid(dentry, uid, 0);
    if (IS_ERR(fid))
        return fid;

    ret = p9_client_walk(fid, 0, NULL, 1);
    return ret;
}

struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
{
    int err;
    struct p9_fid *fid;

    fid = v9fs_fid_clone_with_uid(dentry, 0);
    if (IS_ERR(fid))
        goto error_out;
    /*
     * writeback fid will only be used to write back the
     * dirty pages. We always request for the open fid in read-write
     * mode so that a partial page write which result in page
     * read can work.
     */
    err = p9_client_open(fid, O_RDWR);
    if (err < 0) {
        p9_client_clunk(fid);
        fid = ERR_PTR(err);
        goto error_out;
    }
error_out:
    return fid;
}