C++ GFS2_I函數代碼示例

static int gfs2_readpages(struct file *file, struct address_space *mapping,
			  struct list_head *pages, unsigned nr_pages)
{
	struct inode *inode = mapping->host;
	struct gfs2_inode *ip = GFS2_I(inode);
	struct gfs2_sbd *sdp = GFS2_SB(inode);
	struct gfs2_holder gh;
	int ret;

	gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
	ret = gfs2_glock_nq(&gh);
	if (unlikely(ret))
		goto out_uninit;
	if (!gfs2_is_stuffed(ip))
		ret = mpage_readpages(mapping, pages, nr_pages, gfs2_block_map);
	gfs2_glock_dq(&gh);
out_uninit:
	gfs2_holder_uninit(&gh);
	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
		ret = -EIO;
	return ret;
}

static struct dentry *__gfs2_lookup(struct inode *dir, struct dentry *dentry,
				    struct file *file, int *opened)
{
	struct inode *inode;
	struct dentry *d;
	struct gfs2_holder gh;
	struct gfs2_glock *gl;
	int error;

	inode = gfs2_lookupi(dir, &dentry->d_name, 0);
	if (!inode)
		return NULL;
	if (IS_ERR(inode))
		return ERR_CAST(inode);

	gl = GFS2_I(inode)->i_gl;
	error = gfs2_glock_nq_init(gl, LM_ST_SHARED, LM_FLAG_ANY, &gh);
	if (error) {
		iput(inode);
		return ERR_PTR(error);
	}

	d = d_splice_alias(inode, dentry);
	if (IS_ERR(d)) {
		iput(inode);
		gfs2_glock_dq_uninit(&gh);
		return d;
	}
	if (file && S_ISREG(inode->i_mode))
		error = finish_open(file, dentry, gfs2_open_common, opened);

	gfs2_glock_dq_uninit(&gh);
	if (error) {
		dput(d);
		return ERR_PTR(error);
	}
	return d;
}

static loff_t gfs2_llseek(struct file *file, loff_t offset, int whence)
{
	struct gfs2_inode *ip = GFS2_I(file->f_mapping->host);
	struct gfs2_holder i_gh;
	loff_t error;

	switch (whence) {
	case SEEK_END:
		error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY,
					   &i_gh);
		if (!error) {
			error = generic_file_llseek(file, offset, whence);
			gfs2_glock_dq_uninit(&i_gh);
		}
		break;

	case SEEK_DATA:
		error = gfs2_seek_data(file, offset);
		break;

	case SEEK_HOLE:
		error = gfs2_seek_hole(file, offset);
		break;

	case SEEK_CUR:
	case SEEK_SET:
		/*
		 * These don't reference inode->i_size and don't depend on the
		 * block mapping, so we don't need the glock.
		 */
		error = generic_file_llseek(file, offset, whence);
		break;
	default:
		error = -EINVAL;
	}

	return error;
}

static int gfs2_unlink_inode(struct gfs2_inode *dip,
			     const struct dentry *dentry,
			     struct buffer_head *bh)
{
	struct inode *inode = dentry->d_inode;
	struct gfs2_inode *ip = GFS2_I(inode);
	int error;

	error = gfs2_dir_del(dip, dentry);
	if (error)
		return error;

	ip->i_entries = 0;
	inode->i_ctime = CURRENT_TIME;
	if (S_ISDIR(inode->i_mode))
		clear_nlink(inode);
	else
		drop_nlink(inode);
	mark_inode_dirty(inode);
	if (inode->i_nlink == 0)
		gfs2_unlink_di(inode);
	return 0;
}

static int gfs2_mmap(struct file *file, struct vm_area_struct *vma)
{
	struct gfs2_inode *ip = GFS2_I(file->f_mapping->host);

	if (!(file->f_flags & O_NOATIME) &&
	    !IS_NOATIME(&ip->i_inode)) {
		struct gfs2_holder i_gh;
		int error;

		gfs2_holder_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
		error = gfs2_glock_nq(&i_gh);
		if (error == 0) {
			file_accessed(file);
			gfs2_glock_dq(&i_gh);
		}
		gfs2_holder_uninit(&i_gh);
		if (error)
			return error;
	}
	vma->vm_ops = &gfs2_vm_ops;

	return 0;
}

static void inode_go_inval(struct gfs2_glock *gl, int flags)
{
	struct gfs2_inode *ip = gl->gl_object;

	gfs2_assert_withdraw(gl->gl_sbd, !atomic_read(&gl->gl_ail_count));

	if (flags & DIO_METADATA) {
		struct address_space *mapping = gfs2_glock2aspace(gl);
		truncate_inode_pages(mapping, 0);
		if (ip) {
			set_bit(GIF_INVALID, &ip->i_flags);
			forget_all_cached_acls(&ip->i_inode);
			gfs2_dir_hash_inval(ip);
		}
	}

	if (ip == GFS2_I(gl->gl_sbd->sd_rindex)) {
		gfs2_log_flush(gl->gl_sbd, NULL, NORMAL_FLUSH);
		gl->gl_sbd->sd_rindex_uptodate = 0;
	}
	if (ip && S_ISREG(ip->i_inode.i_mode))
		truncate_inode_pages(ip->i_inode.i_mapping, 0);
}

static struct dentry *gfs2_get_dentry(struct super_block *sb,
				      struct gfs2_inum_host *inum)
{
	struct gfs2_sbd *sdp = sb->s_fs_info;
	struct inode *inode;

	inode = gfs2_ilookup(sb, inum->no_addr);
	if (inode) {
		if (GFS2_I(inode)->i_no_formal_ino != inum->no_formal_ino) {
			iput(inode);
			return ERR_PTR(-ESTALE);
		}
		goto out_inode;
	}

	inode = gfs2_lookup_by_inum(sdp, inum->no_addr, &inum->no_formal_ino,
				    GFS2_BLKST_DINODE);
	if (IS_ERR(inode))
		return ERR_CAST(inode);

out_inode:
	return d_obtain_alias(inode);
}

int gfs2_permission(struct inode *inode, int mask)
{
	struct gfs2_inode *ip = GFS2_I(inode);
	struct gfs2_holder i_gh;
	int error;
	int unlock = 0;

	if (gfs2_glock_is_locked_by_me(ip->i_gl) == NULL) {
		error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY, &i_gh);
		if (error)
			return error;
		unlock = 1;
	}

	if ((mask & MAY_WRITE) && IS_IMMUTABLE(inode))
		error = -EACCES;
	else
		error = generic_permission(inode, mask, gfs2_check_acl);
	if (unlock)
		gfs2_glock_dq_uninit(&i_gh);

	return error;
}

static int do_flock(struct file *file, int cmd, struct file_lock *fl)
{
	struct gfs2_file *fp = file->private_data;
	struct gfs2_holder *fl_gh = &fp->f_fl_gh;
	struct gfs2_inode *ip = GFS2_I(file->f_path.dentry->d_inode);
	struct gfs2_glock *gl;
	unsigned int state;
	int flags;
	int error = 0;

	state = (fl->fl_type == F_WRLCK) ? LM_ST_EXCLUSIVE : LM_ST_SHARED;
	flags = (IS_SETLKW(cmd) ? 0 : LM_FLAG_TRY) | GL_EXACT | GL_NOCACHE;

	mutex_lock(&fp->f_fl_mutex);

	gl = fl_gh->gh_gl;
	if (gl) {
		if (fl_gh->gh_state == state)
			goto out;
		flock_lock_file_wait(file,
				     &(struct file_lock){.fl_type = F_UNLCK});
		gfs2_glock_dq_wait(fl_gh);
		gfs2_holder_reinit(state, flags, fl_gh);
	} else {

static int gfs2_rename(struct inode *odir, struct dentry *odentry,
		       struct inode *ndir, struct dentry *ndentry)
{
	struct gfs2_inode *odip = GFS2_I(odir);
	struct gfs2_inode *ndip = GFS2_I(ndir);
	struct gfs2_inode *ip = GFS2_I(odentry->d_inode);
	struct gfs2_inode *nip = NULL;
	struct gfs2_sbd *sdp = GFS2_SB(odir);
	struct gfs2_holder ghs[5], r_gh;
	struct gfs2_rgrpd *nrgd;
	unsigned int num_gh;
	int dir_rename = 0;
	int alloc_required;
	unsigned int x;
	int error;

	if (ndentry->d_inode) {
		nip = GFS2_I(ndentry->d_inode);
		if (ip == nip)
			return 0;
	}

	/* Make sure we aren't trying to move a dirctory into it's subdir */

	if (S_ISDIR(ip->i_inode.i_mode) && odip != ndip) {
		dir_rename = 1;

		error = gfs2_glock_nq_init(sdp->sd_rename_gl, LM_ST_EXCLUSIVE, 0,
					   &r_gh);
		if (error)
			goto out;

		error = gfs2_ok_to_move(ip, ndip);
		if (error)
			goto out_gunlock_r;
	}

	num_gh = 1;
	gfs2_holder_init(odip->i_gl, LM_ST_EXCLUSIVE, 0, ghs);
	if (odip != ndip) {
		gfs2_holder_init(ndip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
		num_gh++;
	}
	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
	num_gh++;

	if (nip) {
		gfs2_holder_init(nip->i_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh);
		num_gh++;
		/* grab the resource lock for unlink flag twiddling 
		 * this is the case of the target file already existing
		 * so we unlink before doing the rename
		 */
		nrgd = gfs2_blk2rgrpd(sdp, nip->i_no_addr);
		if (nrgd)
			gfs2_holder_init(nrgd->rd_gl, LM_ST_EXCLUSIVE, 0, ghs + num_gh++);
	}

	error = gfs2_glock_nq_m(num_gh, ghs);
	if (error)
		goto out_uninit;

	/* Check out the old directory */

	error = gfs2_unlink_ok(odip, &odentry->d_name, ip);
	if (error)
		goto out_gunlock;

	/* Check out the new directory */

	if (nip) {
		error = gfs2_unlink_ok(ndip, &ndentry->d_name, nip);
		if (error)
			goto out_gunlock;

		if (S_ISDIR(nip->i_inode.i_mode)) {
			if (nip->i_di.di_entries < 2) {
				if (gfs2_consist_inode(nip))
					gfs2_dinode_print(nip);
				error = -EIO;
				goto out_gunlock;
			}
			if (nip->i_di.di_entries > 2) {
				error = -ENOTEMPTY;
				goto out_gunlock;
			}
		}
	} else {
		error = gfs2_permission(ndir, MAY_WRITE | MAY_EXEC);
		if (error)
			goto out_gunlock;

		error = gfs2_dir_check(ndir, &ndentry->d_name, NULL);
		switch (error) {
		case -ENOENT:
			error = 0;
			break;
		case 0:
			error = -EEXIST;
		default:
//.........這裏部分代碼省略.........

struct inode *gfs2_createi(struct gfs2_holder *ghs, const struct qstr *name,
			   unsigned int mode, dev_t dev)
{
	struct inode *inode = NULL;
	struct gfs2_inode *dip = ghs->gh_gl->gl_object;
	struct inode *dir = &dip->i_inode;
	struct gfs2_sbd *sdp = GFS2_SB(&dip->i_inode);
	struct gfs2_inum_host inum = { .no_addr = 0, .no_formal_ino = 0 };
	int error;
	u64 generation;
	struct buffer_head *bh = NULL;

	if (!name->len || name->len > GFS2_FNAMESIZE)
		return ERR_PTR(-ENAMETOOLONG);

	gfs2_holder_reinit(LM_ST_EXCLUSIVE, 0, ghs);
	error = gfs2_glock_nq(ghs);
	if (error)
		goto fail;

	error = create_ok(dip, name, mode);
	if (error)
		goto fail_gunlock;

	error = alloc_dinode(dip, &inum.no_addr, &generation);
	if (error)
		goto fail_gunlock;
	inum.no_formal_ino = generation;

	error = gfs2_glock_nq_num(sdp, inum.no_addr, &gfs2_inode_glops,
				  LM_ST_EXCLUSIVE, GL_SKIP, ghs + 1);
	if (error)
		goto fail_gunlock;

	error = make_dinode(dip, ghs[1].gh_gl, mode, &inum, &generation, dev, &bh);
	if (error)
		goto fail_gunlock2;

	inode = gfs2_inode_lookup(dir->i_sb, IF2DT(mode), inum.no_addr,
				  inum.no_formal_ino);
	if (IS_ERR(inode))
		goto fail_gunlock2;

	error = gfs2_inode_refresh(GFS2_I(inode));
	if (error)
		goto fail_gunlock2;

	error = gfs2_acl_create(dip, inode);
	if (error)
		goto fail_gunlock2;

	error = gfs2_security_init(dip, GFS2_I(inode));
	if (error)
		goto fail_gunlock2;

	error = link_dinode(dip, name, GFS2_I(inode));
	if (error)
		goto fail_gunlock2;

	if (bh)
		brelse(bh);
	return inode;

fail_gunlock2:
	gfs2_glock_dq_uninit(ghs + 1);
	if (inode && !IS_ERR(inode))
		iput(inode);
fail_gunlock:
	gfs2_glock_dq(ghs);
fail:
	if (bh)
		brelse(bh);
	return ERR_PTR(error);
}

static int __gfs2_setattr_simple(struct gfs2_inode *ip, struct iattr *attr)
{
	struct inode *inode = &ip->i_inode;
	struct buffer_head *dibh;
	int error;

	error = gfs2_meta_inode_buffer(ip, &dibh);
	if (error)
		return error;

	if ((attr->ia_valid & ATTR_SIZE) &&
	    attr->ia_size != i_size_read(inode)) {
		error = vmtruncate(inode, attr->ia_size);
		if (error)
			return error;
	}

	setattr_copy(inode, attr);
	mark_inode_dirty(inode);

	gfs2_assert_warn(GFS2_SB(inode), !error);
	gfs2_trans_add_bh(ip->i_gl, dibh, 1);
	gfs2_dinode_out(ip, dibh->b_data);
	brelse(dibh);
	return 0;
//.........這裏部分代碼省略.........

struct inode *gfs2_inode_lookup(struct super_block *sb,
				unsigned int type,
				u64 no_addr,
				u64 no_formal_ino)
{
	struct inode *inode;
	struct gfs2_inode *ip;
	struct gfs2_glock *io_gl = NULL;
	int error;

	inode = gfs2_iget(sb, no_addr);
	ip = GFS2_I(inode);

	if (!inode)
		return ERR_PTR(-ENOBUFS);

	if (inode->i_state & I_NEW) {
		struct gfs2_sbd *sdp = GFS2_SB(inode);
		ip->i_no_formal_ino = no_formal_ino;

		error = gfs2_glock_get(sdp, no_addr, &gfs2_inode_glops, CREATE, &ip->i_gl);
		if (unlikely(error))
			goto fail;
		ip->i_gl->gl_object = ip;

		error = gfs2_glock_get(sdp, no_addr, &gfs2_iopen_glops, CREATE, &io_gl);
		if (unlikely(error))
			goto fail_put;

		set_bit(GIF_INVALID, &ip->i_flags);
		error = gfs2_glock_nq_init(io_gl, LM_ST_SHARED, GL_EXACT, &ip->i_iopen_gh);
		if (unlikely(error))
			goto fail_iopen;
		ip->i_iopen_gh.gh_gl->gl_object = ip;

		gfs2_glock_put(io_gl);
		io_gl = NULL;

		if ((type == DT_UNKNOWN) && (no_formal_ino == 0))
			goto gfs2_nfsbypass;

		inode->i_mode = DT2IF(type);

		/*
		 * We must read the inode in order to work out its type in
		 * this case. Note that this doesn't happen often as we normally
		 * know the type beforehand. This code path only occurs during
		 * unlinked inode recovery (where it is safe to do this glock,
		 * which is not true in the general case).
		 */
		if (type == DT_UNKNOWN) {
			struct gfs2_holder gh;
			error = gfs2_glock_nq_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &gh);
			if (unlikely(error))
				goto fail_glock;
			/* Inode is now uptodate */
			gfs2_glock_dq_uninit(&gh);
		}

		gfs2_set_iop(inode);
	}

gfs2_nfsbypass:
	return inode;
fail_glock:
	gfs2_glock_dq(&ip->i_iopen_gh);
fail_iopen:
	if (io_gl)
		gfs2_glock_put(io_gl);
fail_put:
	if (inode->i_state & I_NEW)
		ip->i_gl->gl_object = NULL;
	gfs2_glock_put(ip->i_gl);
fail:
	if (inode->i_state & I_NEW)
		iget_failed(inode);
	else
		iput(inode);
	return ERR_PTR(error);
}

static int gfs2_write_begin(struct file *file, struct address_space *mapping,
			    loff_t pos, unsigned len, unsigned flags,
			    struct page **pagep, void **fsdata)
{
	struct gfs2_inode *ip = GFS2_I(mapping->host);
	struct gfs2_sbd *sdp = GFS2_SB(mapping->host);
	struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
	unsigned int data_blocks = 0, ind_blocks = 0, rblocks;
	int alloc_required;
	int error = 0;
	struct gfs2_qadata *qa = NULL;
	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
	struct page *page;

	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &ip->i_gh);
	error = gfs2_glock_nq(&ip->i_gh);
	if (unlikely(error))
		goto out_uninit;
	if (&ip->i_inode == sdp->sd_rindex) {
		error = gfs2_glock_nq_init(m_ip->i_gl, LM_ST_EXCLUSIVE,
					   GL_NOCACHE, &m_ip->i_gh);
		if (unlikely(error)) {
			gfs2_glock_dq(&ip->i_gh);
			goto out_uninit;
		}
	}

	alloc_required = gfs2_write_alloc_required(ip, pos, len);

	if (alloc_required || gfs2_is_jdata(ip))
		gfs2_write_calc_reserv(ip, len, &data_blocks, &ind_blocks);

	if (alloc_required) {
		qa = gfs2_qadata_get(ip);
		if (!qa) {
			error = -ENOMEM;
			goto out_unlock;
		}

		error = gfs2_quota_lock_check(ip);
		if (error)
			goto out_alloc_put;

		error = gfs2_inplace_reserve(ip, data_blocks + ind_blocks);
		if (error)
			goto out_qunlock;
	}

	rblocks = RES_DINODE + ind_blocks;
	if (gfs2_is_jdata(ip))
		rblocks += data_blocks ? data_blocks : 1;
	if (ind_blocks || data_blocks)
		rblocks += RES_STATFS + RES_QUOTA;
	if (&ip->i_inode == sdp->sd_rindex)
		rblocks += 2 * RES_STATFS;
	if (alloc_required)
		rblocks += gfs2_rg_blocks(ip);

	error = gfs2_trans_begin(sdp, rblocks,
				 PAGE_CACHE_SIZE/sdp->sd_sb.sb_bsize);
	if (error)
		goto out_trans_fail;

	error = -ENOMEM;
	flags |= AOP_FLAG_NOFS;
	page = grab_cache_page_write_begin(mapping, index, flags);
	*pagep = page;
	if (unlikely(!page))
		goto out_endtrans;

	if (gfs2_is_stuffed(ip)) {
		error = 0;
		if (pos + len > sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode)) {
			error = gfs2_unstuff_dinode(ip, page);
			if (error == 0)
				goto prepare_write;
		} else if (!PageUptodate(page)) {
			error = stuffed_readpage(ip, page);
		}
		goto out;
	}

prepare_write:
	error = __block_write_begin(page, from, len, gfs2_block_map);
out:
	if (error == 0)
		return 0;

	unlock_page(page);
	page_cache_release(page);

	gfs2_trans_end(sdp);
	if (pos + len > ip->i_inode.i_size)
		gfs2_trim_blocks(&ip->i_inode);
	goto out_trans_fail;

out_endtrans:
	gfs2_trans_end(sdp);
out_trans_fail:
//.........這裏部分代碼省略.........

static int gfs2_write_begin(struct file *file, struct address_space *mapping,
			    loff_t pos, unsigned len, unsigned flags,
			    struct page **pagep, void **fsdata)
{
	struct gfs2_inode *ip = GFS2_I(mapping->host);
	struct gfs2_sbd *sdp = GFS2_SB(mapping->host);
	struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
	unsigned int data_blocks = 0, ind_blocks = 0, rblocks;
	unsigned requested = 0;
	int alloc_required;
	int error = 0;
	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
	unsigned from = pos & (PAGE_CACHE_SIZE - 1);
	struct page *page;

	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &ip->i_gh);
	error = gfs2_glock_nq(&ip->i_gh);
	if (unlikely(error))
		goto out_uninit;
	if (&ip->i_inode == sdp->sd_rindex) {
		error = gfs2_glock_nq_init(m_ip->i_gl, LM_ST_EXCLUSIVE,
					   GL_NOCACHE, &m_ip->i_gh);
		if (unlikely(error)) {
			gfs2_glock_dq(&ip->i_gh);
			goto out_uninit;
		}
	}

	alloc_required = gfs2_write_alloc_required(ip, pos, len);

	if (alloc_required || gfs2_is_jdata(ip))
		gfs2_write_calc_reserv(ip, len, &data_blocks, &ind_blocks);

	if (alloc_required) {
		struct gfs2_alloc_parms ap = { .aflags = 0, };
		requested = data_blocks + ind_blocks;
		ap.target = requested;
		error = gfs2_quota_lock_check(ip, &ap);
		if (error)
			goto out_unlock;

		error = gfs2_inplace_reserve(ip, &ap);
		if (error)
			goto out_qunlock;
	}

	rblocks = RES_DINODE + ind_blocks;
	if (gfs2_is_jdata(ip))
		rblocks += data_blocks ? data_blocks : 1;
	if (ind_blocks || data_blocks)
		rblocks += RES_STATFS + RES_QUOTA;
	if (&ip->i_inode == sdp->sd_rindex)
		rblocks += 2 * RES_STATFS;
	if (alloc_required)
		rblocks += gfs2_rg_blocks(ip, requested);

	error = gfs2_trans_begin(sdp, rblocks,
				 PAGE_CACHE_SIZE/sdp->sd_sb.sb_bsize);
	if (error)
		goto out_trans_fail;

	error = -ENOMEM;
	flags |= AOP_FLAG_NOFS;
	page = grab_cache_page_write_begin(mapping, index, flags);
	*pagep = page;
	if (unlikely(!page))
		goto out_endtrans;

	if (gfs2_is_stuffed(ip)) {
		error = 0;
		if (pos + len > sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode)) {
			error = gfs2_unstuff_dinode(ip, page);
			if (error == 0)
				goto prepare_write;
		} else if (!PageUptodate(page)) {
			error = stuffed_readpage(ip, page);
		}
		goto out;
	}

prepare_write:
	error = __block_write_begin(page, from, len, gfs2_block_map);
out:
	if (error == 0)
		return 0;

	unlock_page(page);
	page_cache_release(page);

	gfs2_trans_end(sdp);
	if (pos + len > ip->i_inode.i_size)
		gfs2_trim_blocks(&ip->i_inode);
	goto out_trans_fail;

out_endtrans:
	gfs2_trans_end(sdp);
out_trans_fail:
	if (alloc_required) {
		gfs2_inplace_release(ip);
out_qunlock:
//.........這裏部分代碼省略.........

static ssize_t gfs2_direct_IO(int rw, struct kiocb *iocb,
			      const struct iovec *iov, loff_t offset,
			      unsigned long nr_segs)
{
	struct file *file = iocb->ki_filp;
	struct inode *inode = file->f_mapping->host;
	struct address_space *mapping = inode->i_mapping;
	struct gfs2_inode *ip = GFS2_I(inode);
	struct gfs2_holder gh;
	int rv;

	/*
	 * Deferred lock, even if its a write, since we do no allocation
	 * on this path. All we need change is atime, and this lock mode
	 * ensures that other nodes have flushed their buffered read caches
	 * (i.e. their page cache entries for this inode). We do not,
	 * unfortunately have the option of only flushing a range like
	 * the VFS does.
	 */
	gfs2_holder_init(ip->i_gl, LM_ST_DEFERRED, 0, &gh);
	rv = gfs2_glock_nq(&gh);
	if (rv)
		return rv;
	rv = gfs2_ok_for_dio(ip, rw, offset);
	if (rv != 1)
		goto out; /* dio not valid, fall back to buffered i/o */

	/*
	 * Now since we are holding a deferred (CW) lock at this point, you
	 * might be wondering why this is ever needed. There is a case however
	 * where we've granted a deferred local lock against a cached exclusive
	 * glock. That is ok provided all granted local locks are deferred, but
	 * it also means that it is possible to encounter pages which are
	 * cached and possibly also mapped. So here we check for that and sort
	 * them out ahead of the dio. The glock state machine will take care of
	 * everything else.
	 *
	 * If in fact the cached glock state (gl->gl_state) is deferred (CW) in
	 * the first place, mapping->nr_pages will always be zero.
	 */
	if (mapping->nrpages) {
		loff_t lstart = offset & (PAGE_CACHE_SIZE - 1);
		loff_t len = iov_length(iov, nr_segs);
		loff_t end = PAGE_ALIGN(offset + len) - 1;

		rv = 0;
		if (len == 0)
			goto out;
		if (test_and_clear_bit(GIF_SW_PAGED, &ip->i_flags))
			unmap_shared_mapping_range(ip->i_inode.i_mapping, offset, len);
		rv = filemap_write_and_wait_range(mapping, lstart, end);
		if (rv)
			goto out;
		if (rw == WRITE)
			truncate_inode_pages_range(mapping, lstart, end);
	}

	rv = __blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
				  offset, nr_segs, gfs2_get_block_direct,
				  NULL, NULL, 0);
out:
	gfs2_glock_dq(&gh);
	gfs2_holder_uninit(&gh);
	return rv;
}