Index: uspace/srv/vfs/vfs_ops.c
===================================================================
--- uspace/srv/vfs/vfs_ops.c	(revision 861e7d17d96cb83a483323d486c1da00a6346431)
+++ uspace/srv/vfs/vfs_ops.c	(revision 861e7d17d96cb83a483323d486c1da00a6346431)
@@ -0,0 +1,1068 @@
+/*
+ * Copyright (c) 2008 Jakub Jermar
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/** @addtogroup fs
+ * @{
+ */ 
+
+/**
+ * @file	vfs_ops.c
+ * @brief	Operations that VFS offers to its clients.
+ */
+
+#include <ipc/ipc.h>
+#include <ipc/services.h>
+#include <async.h>
+#include <fibril.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <bool.h>
+#include <futex.h>
+#include <rwlock.h>
+#include <libadt/list.h>
+#include <unistd.h>
+#include <ctype.h>
+#include <as.h>
+#include <assert.h>
+#include <atomic.h>
+#include "vfs.h"
+
+#define min(a, b)	((a) < (b) ? (a) : (b))
+
+/**
+ * This rwlock prevents the race between a triplet-to-VFS-node resolution and a
+ * concurrent VFS operation which modifies the file system namespace.
+ */
+RWLOCK_INITIALIZE(namespace_rwlock);
+
+atomic_t plb_futex = FUTEX_INITIALIZER;
+link_t plb_head;	/**< PLB entry ring buffer. */
+uint8_t *plb = NULL;
+
+/** Perform a path lookup.
+ *
+ * @param path		Path to be resolved; it needn't be an ASCIIZ string.
+ * @param len		Number of path characters pointed by path.
+ * @param result	Empty node structure where the result will be stored.
+ * @param size		Storage where the size of the node will be stored. Can
+ *			be NULL.
+ * @param altroot	If non-empty, will be used instead of rootfs as the root
+ *			of the whole VFS tree.
+ *
+ * @return		EOK on success or an error code from errno.h.
+ */
+int vfs_lookup_internal(char *path, size_t len, vfs_triplet_t *result,
+    size_t *size, vfs_pair_t *altroot)
+{
+	vfs_pair_t *root;
+
+	if (!len)
+		return EINVAL;
+
+	if (altroot)
+		root = altroot;
+	else
+		root = (vfs_pair_t *) &rootfs;
+
+	if (!root->fs_handle)
+		return ENOENT;
+	
+	futex_down(&plb_futex);
+
+	plb_entry_t entry;
+	link_initialize(&entry.plb_link);
+	entry.len = len;
+
+	off_t first;	/* the first free index */
+	off_t last;	/* the last free index */
+
+	if (list_empty(&plb_head)) {
+		first = 0;
+		last = PLB_SIZE - 1;
+	} else {
+		plb_entry_t *oldest = list_get_instance(plb_head.next,
+		    plb_entry_t, plb_link);
+		plb_entry_t *newest = list_get_instance(plb_head.prev,
+		    plb_entry_t, plb_link);
+
+		first = (newest->index + newest->len) % PLB_SIZE;
+		last = (oldest->index - 1) % PLB_SIZE;
+	}
+
+	if (first <= last) {
+		if ((last - first) + 1 < len) {
+			/*
+			 * The buffer cannot absorb the path.
+			 */
+			futex_up(&plb_futex);
+			return ELIMIT;
+		}
+	} else {
+		if (PLB_SIZE - ((first - last) + 1) < len) {
+			/*
+			 * The buffer cannot absorb the path.
+			 */
+			futex_up(&plb_futex);
+			return ELIMIT;
+		}
+	}
+
+	/*
+	 * We know the first free index in PLB and we also know that there is
+	 * enough space in the buffer to hold our path.
+	 */
+
+	entry.index = first;
+	entry.len = len;
+
+	/*
+	 * Claim PLB space by inserting the entry into the PLB entry ring
+	 * buffer.
+	 */
+	list_append(&entry.plb_link, &plb_head);
+	
+	futex_up(&plb_futex);
+
+	/*
+	 * Copy the path into PLB.
+	 */
+	size_t cnt1 = min(len, (PLB_SIZE - first) + 1);
+	size_t cnt2 = len - cnt1;
+	
+	memcpy(&plb[first], path, cnt1);
+	memcpy(plb, &path[cnt1], cnt2);
+
+	ipc_call_t answer;
+	int phone = vfs_grab_phone(root->fs_handle);
+	aid_t req = async_send_3(phone, VFS_LOOKUP, (ipcarg_t) first,
+	    (ipcarg_t) (first + len - 1) % PLB_SIZE,
+	    (ipcarg_t) root->dev_handle, &answer);
+	vfs_release_phone(phone);
+
+	ipcarg_t rc;
+	async_wait_for(req, &rc);
+
+	futex_down(&plb_futex);
+	list_remove(&entry.plb_link);
+	/*
+	 * Erasing the path from PLB will come handy for debugging purposes.
+	 */
+	memset(&plb[first], 0, cnt1);
+	memset(plb, 0, cnt2);
+	futex_up(&plb_futex);
+
+	if (rc == EOK) {
+		result->fs_handle = (int) IPC_GET_ARG1(answer);
+		result->dev_handle = (int) IPC_GET_ARG2(answer);
+		result->index = (int) IPC_GET_ARG3(answer);
+		if (size)
+			*size = (size_t) IPC_GET_ARG4(answer);
+	}
+
+	return rc;
+}
+
+atomic_t rootfs_futex = FUTEX_INITIALIZER;
+vfs_triplet_t rootfs = {
+	.fs_handle = 0,
+	.dev_handle = 0,
+	.index = 0,
+};
+
+static int lookup_root(int fs_handle, int dev_handle, vfs_triplet_t *root,
+    size_t *size)
+{
+	vfs_pair_t altroot = {
+		.fs_handle = fs_handle,
+		.dev_handle = dev_handle,
+	};
+
+	return vfs_lookup_internal("/", strlen("/"), root, size, &altroot);
+}
+
+void vfs_mount(ipc_callid_t rid, ipc_call_t *request)
+{
+	int dev_handle;
+	vfs_node_t *mp_node = NULL;
+
+	/*
+	 * We expect the library to do the device-name to device-handle
+	 * translation for us, thus the device handle will arrive as ARG1
+	 * in the request.
+	 */
+	dev_handle = IPC_GET_ARG1(*request);
+
+	/*
+	 * For now, don't make use of ARG2 and ARG3, but they can be used to
+	 * carry mount options in the future.
+	 */
+
+	ipc_callid_t callid;
+	size_t size;
+
+	/*
+	 * Now, we expect the client to send us data with the name of the file
+	 * system.
+	 */
+	if (!ipc_data_write_receive(&callid, &size)) {
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+
+	/*
+	 * Don't receive more than is necessary for storing a full file system
+	 * name.
+	 */
+	if (size < 1 || size > FS_NAME_MAXLEN) {
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+
+	/*
+	 * Deliver the file system name.
+	 */
+	char fs_name[FS_NAME_MAXLEN + 1];
+	(void) ipc_data_write_finalize(callid, fs_name, size);
+	fs_name[size] = '\0';
+	
+	/*
+	 * Check if we know a file system with the same name as is in fs_name.
+	 * This will also give us its file system handle.
+	 */
+	int fs_handle = fs_name_to_handle(fs_name, true);
+	if (!fs_handle) {
+		ipc_answer_0(rid, ENOENT);
+		return;
+	}
+
+	/*
+	 * Now, we want the client to send us the mount point.
+	 */
+	if (!ipc_data_write_receive(&callid, &size)) {
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+
+	/*
+	 * Check whether size is reasonable wrt. the mount point.
+	 */
+	if (size < 1 || size > MAX_PATH_LEN) {
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+	/*
+	 * Allocate buffer for the mount point data being received.
+	 */
+	uint8_t *buf;
+	buf = malloc(size);
+	if (!buf) {
+		ipc_answer_0(callid, ENOMEM);
+		ipc_answer_0(rid, ENOMEM);
+		return;
+	}
+
+	/*
+	 * Deliver the mount point.
+	 */
+	(void) ipc_data_write_finalize(callid, buf, size);
+
+	/*
+	 * Lookup the root node of the filesystem being mounted.
+	 * In this case, we don't need to take the namespace_futex as the root
+	 * node cannot be removed. However, we do take a reference to it so
+	 * that we can track how many times it has been mounted.
+	 */
+	int rc;
+	vfs_triplet_t mounted_root;
+	size_t mrsz;
+	rc = lookup_root(fs_handle, dev_handle, &mounted_root, &mrsz);
+	if (rc != EOK) {
+		free(buf);
+		ipc_answer_0(rid, rc);
+		return;
+	}
+	vfs_node_t *mr_node = vfs_node_get(&mounted_root, mrsz);
+	if (!mr_node) {
+		free(buf);
+		ipc_answer_0(rid, ENOMEM);
+		return;
+	}
+
+	/*
+	 * Finally, we need to resolve the path to the mountpoint. 
+	 */
+	vfs_triplet_t mp;
+	size_t mpsz;
+	futex_down(&rootfs_futex);
+	if (rootfs.fs_handle) {
+		/*
+		 * We already have the root FS.
+		 */
+		rwlock_write_lock(&namespace_rwlock);
+		rc = vfs_lookup_internal(buf, size, &mp, &mpsz, NULL);
+		if (rc != EOK) {
+			/*
+			 * The lookup failed for some reason.
+			 */
+			rwlock_write_unlock(&namespace_rwlock);
+			futex_up(&rootfs_futex);
+			vfs_node_put(mr_node);	/* failed -> drop reference */
+			free(buf);
+			ipc_answer_0(rid, rc);
+			return;
+		}
+		mp_node = vfs_node_get(&mp, mpsz);
+		if (!mp_node) {
+			rwlock_write_unlock(&namespace_rwlock);
+			futex_up(&rootfs_futex);
+			vfs_node_put(mr_node);	/* failed -> drop reference */
+			free(buf);
+			ipc_answer_0(rid, ENOMEM);
+			return;
+		}
+		/*
+		 * Now we hold a reference to mp_node.
+		 * It will be dropped upon the corresponding VFS_UNMOUNT.
+		 * This prevents the mount point from being deleted.
+		 */
+		rwlock_write_unlock(&namespace_rwlock);
+	} else {
+		/*
+		 * We still don't have the root file system mounted.
+		 */
+		if ((size == 1) && (buf[0] == '/')) {
+			/*
+			 * For this simple, but important case, we are done.
+			 */
+			rootfs = mounted_root;
+			futex_up(&rootfs_futex);
+			free(buf);
+			ipc_answer_0(rid, EOK);
+			return;
+		} else {
+			/*
+			 * We can't resolve this without the root filesystem
+			 * being mounted first.
+			 */
+			futex_up(&rootfs_futex);
+			free(buf);
+			vfs_node_put(mr_node);	/* failed -> drop reference */
+			ipc_answer_0(rid, ENOENT);
+			return;
+		}
+	}
+	futex_up(&rootfs_futex);
+	
+	free(buf);	/* The buffer is not needed anymore. */
+	
+	/*
+	 * At this point, we have all necessary pieces: file system and device
+	 * handles, and we know the mount point VFS node and also the root node
+	 * of the file system being mounted.
+	 */
+
+	int phone = vfs_grab_phone(mp.fs_handle);
+	/* Later we can use ARG3 to pass mode/flags. */
+	aid_t req1 = async_send_3(phone, VFS_MOUNT, (ipcarg_t) mp.dev_handle,
+	    (ipcarg_t) mp.index, 0, NULL);
+	/* The second call uses the same method. */
+	aid_t req2 = async_send_3(phone, VFS_MOUNT,
+	    (ipcarg_t) mounted_root.fs_handle,
+	    (ipcarg_t) mounted_root.dev_handle, (ipcarg_t) mounted_root.index,
+	    NULL);
+	vfs_release_phone(phone);
+
+	ipcarg_t rc1;
+	ipcarg_t rc2;
+	async_wait_for(req1, &rc1);
+	async_wait_for(req2, &rc2);
+
+	if ((rc1 != EOK) || (rc2 != EOK)) {
+		/* Mount failed, drop references to mr_node and mp_node. */
+		vfs_node_put(mr_node);
+		if (mp_node)
+			vfs_node_put(mp_node);
+	}
+	
+	if (rc2 == EOK)
+		ipc_answer_0(rid, rc1);
+	else if (rc1 == EOK)
+		ipc_answer_0(rid, rc2);
+	else
+		ipc_answer_0(rid, rc1);
+}
+
+void vfs_open(ipc_callid_t rid, ipc_call_t *request)
+{
+	if (!vfs_files_init()) {
+		ipc_answer_0(rid, ENOMEM);
+		return;
+	}
+
+	/*
+	 * The POSIX interface is open(path, flags, mode).
+	 * We can receive flags and mode along with the VFS_OPEN call; the path
+	 * will need to arrive in another call.
+	 */
+	int flags = IPC_GET_ARG1(*request);
+	int mode = IPC_GET_ARG2(*request);
+	size_t len;
+
+	ipc_callid_t callid;
+
+	if (!ipc_data_write_receive(&callid, &len)) {
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+
+	/*
+	 * Now we are on the verge of accepting the path.
+	 *
+	 * There is one optimization we could do in the future: copy the path
+	 * directly into the PLB using some kind of a callback.
+	 */
+	char *path = malloc(len);
+	
+	if (!path) {
+		ipc_answer_0(callid, ENOMEM);
+		ipc_answer_0(rid, ENOMEM);
+		return;
+	}
+
+	int rc;
+	if ((rc = ipc_data_write_finalize(callid, path, len))) {
+		ipc_answer_0(rid, rc);
+		free(path);
+		return;
+	}
+	
+	/*
+	 * Avoid the race condition in which the file can be deleted before we
+	 * find/create-and-lock the VFS node corresponding to the looked-up
+	 * triplet.
+	 */
+	rwlock_read_lock(&namespace_rwlock);
+
+	/*
+	 * The path is now populated and we can call vfs_lookup_internal().
+	 */
+	vfs_triplet_t triplet;
+	size_t size;
+	rc = vfs_lookup_internal(path, len, &triplet, &size, NULL);
+	if (rc) {
+		rwlock_read_unlock(&namespace_rwlock);
+		ipc_answer_0(rid, rc);
+		free(path);
+		return;
+	}
+
+	/*
+	 * Path is no longer needed.
+	 */
+	free(path);
+
+	vfs_node_t *node = vfs_node_get(&triplet, size);
+	rwlock_read_unlock(&namespace_rwlock);
+
+	/*
+	 * Get ourselves a file descriptor and the corresponding vfs_file_t
+	 * structure.
+	 */
+	int fd = vfs_fd_alloc();
+	if (fd < 0) {
+		vfs_node_put(node);
+		ipc_answer_0(rid, fd);
+		return;
+	}
+	vfs_file_t *file = vfs_file_get(fd);
+	file->node = node;
+
+	/*
+	 * The following increase in reference count is for the fact that the
+	 * file is being opened and that a file structure is pointing to it.
+	 * It is necessary so that the file will not disappear when
+	 * vfs_node_put() is called. The reference will be dropped by the
+	 * respective VFS_CLOSE.
+	 */
+	vfs_node_addref(node);
+	vfs_node_put(node);
+
+	/*
+	 * Success! Return the new file descriptor to the client.
+	 */
+	ipc_answer_1(rid, EOK, fd);
+}
+
+static void vfs_rdwr(ipc_callid_t rid, ipc_call_t *request, bool read)
+{
+
+	/*
+	 * The following code strongly depends on the fact that the files data
+	 * structure can be only accessed by a single fibril and all file
+	 * operations are serialized (i.e. the reads and writes cannot
+	 * interleave and a file cannot be closed while it is being read).
+	 *
+	 * Additional synchronization needs to be added once the table of
+	 * open files supports parallel access!
+	 */
+
+	int fd = IPC_GET_ARG1(*request);
+
+	/*
+	 * Lookup the file structure corresponding to the file descriptor.
+	 */
+	vfs_file_t *file = vfs_file_get(fd);
+	if (!file) {
+		ipc_answer_0(rid, ENOENT);
+		return;
+	}
+
+	/*
+	 * Now we need to receive a call with client's
+	 * IPC_M_DATA_READ/IPC_M_DATA_WRITE request.
+	 */
+	ipc_callid_t callid;
+	int res;
+	if (read)
+		res = ipc_data_read_receive(&callid, NULL);
+	else 
+		res = ipc_data_write_receive(&callid, NULL);
+	if (!res) {
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+
+	/*
+	 * Lock the open file structure so that no other thread can manipulate
+	 * the same open file at a time.
+	 */
+	futex_down(&file->lock);
+
+	/*
+	 * Lock the file's node so that no other client can read/write to it at
+	 * the same time.
+	 */
+	if (read)
+		rwlock_read_lock(&file->node->contents_rwlock);
+	else
+		rwlock_write_lock(&file->node->contents_rwlock);
+
+	int fs_phone = vfs_grab_phone(file->node->fs_handle);	
+	
+	/*
+	 * Make a VFS_READ/VFS_WRITE request at the destination FS server.
+	 */
+	aid_t msg;
+	ipc_call_t answer;
+	msg = async_send_3(fs_phone, IPC_GET_METHOD(*request),
+	    file->node->dev_handle, file->node->index, file->pos, &answer);
+	
+	/*
+	 * Forward the IPC_M_DATA_READ/IPC_M_DATA_WRITE request to the
+	 * destination FS server. The call will be routed as if sent by
+	 * ourselves. Note that call arguments are immutable in this case so we
+	 * don't have to bother.
+	 */
+	ipc_forward_fast(callid, fs_phone, 0, 0, 0, IPC_FF_ROUTE_FROM_ME);
+
+	vfs_release_phone(fs_phone);
+
+	/*
+	 * Wait for reply from the FS server.
+	 */
+	ipcarg_t rc;
+	async_wait_for(msg, &rc);
+	size_t bytes = IPC_GET_ARG1(answer);
+
+	/*
+	 * Unlock the VFS node.
+	 */
+	if (read)
+		rwlock_read_unlock(&file->node->contents_rwlock);
+	else {
+		/* Update the cached version of node's size. */
+		file->node->size = IPC_GET_ARG2(answer); 
+		rwlock_write_unlock(&file->node->contents_rwlock);
+	}
+
+	/*
+	 * Update the position pointer and unlock the open file.
+	 */
+	file->pos += bytes;
+	futex_up(&file->lock);
+
+	/*
+	 * FS server's reply is the final result of the whole operation we
+	 * return to the client.
+	 */
+	ipc_answer_1(rid, rc, bytes);
+}
+
+void vfs_read(ipc_callid_t rid, ipc_call_t *request)
+{
+	vfs_rdwr(rid, request, true);
+}
+
+void vfs_write(ipc_callid_t rid, ipc_call_t *request)
+{
+	vfs_rdwr(rid, request, false);
+}
+
+void vfs_seek(ipc_callid_t rid, ipc_call_t *request)
+{
+	int fd = (int) IPC_GET_ARG1(*request);
+	off_t off = (off_t) IPC_GET_ARG2(*request);
+	int whence = (int) IPC_GET_ARG3(*request);
+
+
+	/*
+	 * Lookup the file structure corresponding to the file descriptor.
+	 */
+	vfs_file_t *file = vfs_file_get(fd);
+	if (!file) {
+		ipc_answer_0(rid, ENOENT);
+		return;
+	}
+
+	off_t newpos;
+	futex_down(&file->lock);
+	if (whence == SEEK_SET) {
+		file->pos = off;
+		futex_up(&file->lock);
+		ipc_answer_1(rid, EOK, off);
+		return;
+	}
+	if (whence == SEEK_CUR) {
+		if (file->pos + off < file->pos) {
+			futex_up(&file->lock);
+			ipc_answer_0(rid, EOVERFLOW);
+			return;
+		}
+		file->pos += off;
+		newpos = file->pos;
+		futex_up(&file->lock);
+		ipc_answer_1(rid, EOK, newpos);
+		return;
+	}
+	if (whence == SEEK_END) {
+		rwlock_read_lock(&file->node->contents_rwlock);
+		size_t size = file->node->size;
+		rwlock_read_unlock(&file->node->contents_rwlock);
+		if (size + off < size) {
+			futex_up(&file->lock);
+			ipc_answer_0(rid, EOVERFLOW);
+			return;
+		}
+		newpos = size + off;
+		futex_up(&file->lock);
+		ipc_answer_1(rid, EOK, newpos);
+		return;
+	}
+	futex_up(&file->lock);
+	ipc_answer_0(rid, EINVAL);
+}
+
+atomic_t fs_head_futex = FUTEX_INITIALIZER;
+link_t fs_head;
+
+atomic_t fs_handle_next = {
+	.count = 1
+};
+
+/** Verify the VFS info structure.
+ *
+ * @param info		Info structure to be verified.
+ *
+ * @return		Non-zero if the info structure is sane, zero otherwise.
+ */
+static bool vfs_info_sane(vfs_info_t *info)
+{
+	int i;
+
+	/*
+	 * Check if the name is non-empty and is composed solely of ASCII
+	 * characters [a-z]+[a-z0-9_-]*.
+	 */
+	if (!islower(info->name[0])) {
+		dprintf("The name doesn't start with a lowercase character.\n");
+		return false;
+	}
+	for (i = 1; i < FS_NAME_MAXLEN; i++) {
+		if (!(islower(info->name[i]) || isdigit(info->name[i])) &&
+		    (info->name[i] != '-') && (info->name[i] != '_')) {
+			if (info->name[i] == '\0') {
+				break;
+			} else {
+				dprintf("The name contains illegal "
+				    "characters.\n");
+				return false;
+			}
+		}
+	}
+	/*
+	 * This check is not redundant. It ensures that the name is
+	 * NULL-terminated, even if FS_NAME_MAXLEN characters are used.
+	 */
+	if (info->name[i] != '\0') {
+		dprintf("The name is not properly NULL-terminated.\n");	
+		return false;
+	}
+	
+
+	/*
+	 * Check if the FS implements mandatory VFS operations.
+	 */
+	if (info->ops[IPC_METHOD_TO_VFS_OP(VFS_REGISTER)] != VFS_OP_DEFINED) {
+		dprintf("Operation VFS_REGISTER not defined by the client.\n");
+		return false;
+	}
+	if (info->ops[IPC_METHOD_TO_VFS_OP(VFS_MOUNT)] != VFS_OP_DEFINED) {
+		dprintf("Operation VFS_MOUNT not defined by the client.\n");
+		return false;
+	}
+	if (info->ops[IPC_METHOD_TO_VFS_OP(VFS_UNMOUNT)] != VFS_OP_DEFINED) {
+		dprintf("Operation VFS_UNMOUNT not defined by the client.\n");
+		return false;
+	}
+	if (info->ops[IPC_METHOD_TO_VFS_OP(VFS_LOOKUP)] != VFS_OP_DEFINED) {
+		dprintf("Operation VFS_LOOKUP not defined by the client.\n");
+		return false;
+	}
+	if (info->ops[IPC_METHOD_TO_VFS_OP(VFS_OPEN)] != VFS_OP_DEFINED) {
+		dprintf("Operation VFS_OPEN not defined by the client.\n");
+		return false;
+	}
+	if (info->ops[IPC_METHOD_TO_VFS_OP(VFS_CLOSE)] != VFS_OP_DEFINED) {
+		dprintf("Operation VFS_CLOSE not defined by the client.\n");
+		return false;
+	}
+	if (info->ops[IPC_METHOD_TO_VFS_OP(VFS_READ)] != VFS_OP_DEFINED) {
+		dprintf("Operation VFS_READ not defined by the client.\n");
+		return false;
+	}
+	
+	/*
+	 * Check if each operation is either not defined, defined or default.
+	 */
+	for (i = VFS_FIRST; i < VFS_LAST; i++) {
+		if ((info->ops[IPC_METHOD_TO_VFS_OP(i)] != VFS_OP_NULL) && 
+		    (info->ops[IPC_METHOD_TO_VFS_OP(i)] != VFS_OP_DEFAULT) && 
+		    (info->ops[IPC_METHOD_TO_VFS_OP(i)] != VFS_OP_DEFINED)) {
+			dprintf("Operation info not understood.\n");
+			return false;
+		}
+	}
+	return true;
+}
+
+/** VFS_REGISTER protocol function.
+ *
+ * @param rid		Hash of the call with the request.
+ * @param request	Call structure with the request.
+ */
+void vfs_register(ipc_callid_t rid, ipc_call_t *request)
+{
+	ipc_callid_t callid;
+	ipc_call_t call;
+	int rc;
+	size_t size;
+
+	dprintf("Processing VFS_REGISTER request received from %p.\n",
+	    request->in_phone_hash);
+
+	/*
+	 * The first call has to be IPC_M_DATA_SEND in which we receive the
+	 * VFS info structure from the client FS.
+	 */
+	if (!ipc_data_write_receive(&callid, &size)) {
+		/*
+		 * The client doesn't obey the same protocol as we do.
+		 */
+		dprintf("Receiving of VFS info failed.\n");
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+	
+	dprintf("VFS info received, size = %d\n", size);
+	
+	/*
+	 * We know the size of the VFS info structure. See if the client
+	 * understands this easy concept too.
+	 */
+	if (size != sizeof(vfs_info_t)) {
+		/*
+		 * The client is sending us something, which cannot be
+		 * the info structure.
+		 */
+		dprintf("Received VFS info has bad size.\n");
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+
+	/*
+	 * Allocate and initialize a buffer for the fs_info structure.
+	 */
+	fs_info_t *fs_info;
+	fs_info = (fs_info_t *) malloc(sizeof(fs_info_t));
+	if (!fs_info) {
+		dprintf("Could not allocate memory for FS info.\n");
+		ipc_answer_0(callid, ENOMEM);
+		ipc_answer_0(rid, ENOMEM);
+		return;
+	}
+	link_initialize(&fs_info->fs_link);
+	futex_initialize(&fs_info->phone_futex, 1);
+		
+	rc = ipc_data_write_finalize(callid, &fs_info->vfs_info, size);
+	if (rc != EOK) {
+		dprintf("Failed to deliver the VFS info into our AS, rc=%d.\n",
+		    rc);
+		free(fs_info);
+		ipc_answer_0(callid, rc);
+		ipc_answer_0(rid, rc);
+		return;
+	}
+
+	dprintf("VFS info delivered.\n");
+		
+	if (!vfs_info_sane(&fs_info->vfs_info)) {
+		free(fs_info);
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+		
+	futex_down(&fs_head_futex);
+
+	/*
+	 * Check for duplicit registrations.
+	 */
+	if (fs_name_to_handle(fs_info->vfs_info.name, false)) {
+		/*
+		 * We already register a fs like this.
+		 */
+		dprintf("FS is already registered.\n");
+		futex_up(&fs_head_futex);
+		free(fs_info);
+		ipc_answer_0(callid, EEXISTS);
+		ipc_answer_0(rid, EEXISTS);
+		return;
+	}
+
+	/*
+	 * Add fs_info to the list of registered FS's.
+	 */
+	dprintf("Inserting FS into the list of registered file systems.\n");
+	list_append(&fs_info->fs_link, &fs_head);
+
+	/*
+	 * Now we want the client to send us the IPC_M_CONNECT_TO_ME call so
+	 * that a callback connection is created and we have a phone through
+	 * which to forward VFS requests to it.
+	 */
+	callid = async_get_call(&call);
+	if (IPC_GET_METHOD(call) != IPC_M_CONNECT_TO_ME) {
+		dprintf("Unexpected call, method = %d\n", IPC_GET_METHOD(call));
+		list_remove(&fs_info->fs_link);
+		futex_up(&fs_head_futex);
+		free(fs_info);
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+	fs_info->phone = IPC_GET_ARG5(call);
+	ipc_answer_0(callid, EOK);
+
+	dprintf("Callback connection to FS created.\n");
+
+	/*
+	 * The client will want us to send him the address space area with PLB.
+	 */
+
+	if (!ipc_share_in_receive(&callid, &size)) {
+		dprintf("Unexpected call, method = %d\n", IPC_GET_METHOD(call));
+		list_remove(&fs_info->fs_link);
+		futex_up(&fs_head_futex);
+		ipc_hangup(fs_info->phone);
+		free(fs_info);
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+	
+	/*
+	 * We can only send the client address space area PLB_SIZE bytes long.
+	 */
+	if (size != PLB_SIZE) {
+		dprintf("Client suggests wrong size of PFB, size = %d\n", size);
+		list_remove(&fs_info->fs_link);
+		futex_up(&fs_head_futex);
+		ipc_hangup(fs_info->phone);
+		free(fs_info);
+		ipc_answer_0(callid, EINVAL);
+		ipc_answer_0(rid, EINVAL);
+		return;
+	}
+
+	/*
+	 * Commit to read-only sharing the PLB with the client.
+	 */
+	(void) ipc_share_in_finalize(callid, plb,
+	    AS_AREA_READ | AS_AREA_CACHEABLE);
+
+	dprintf("Sharing PLB.\n");
+
+	/*
+	 * That was it. The FS has been registered.
+	 * In reply to the VFS_REGISTER request, we assign the client file
+	 * system a global file system handle.
+	 */
+	fs_info->fs_handle = (int) atomic_postinc(&fs_handle_next);
+	ipc_answer_1(rid, EOK, (ipcarg_t) fs_info->fs_handle);
+	
+	futex_up(&fs_head_futex);
+	
+	dprintf("\"%.*s\" filesystem successfully registered, handle=%d.\n",
+	    FS_NAME_MAXLEN, fs_info->vfs_info.name, fs_info->fs_handle);
+}
+
+/** For a given file system handle, implement policy for allocating a phone.
+ *
+ * @param handle	File system handle.
+ *
+ * @return		Phone over which a multi-call request can be safely
+ *			sent. Return 0 if no phone was found.
+ */
+int vfs_grab_phone(int handle)
+{
+	/*
+	 * For now, we don't try to be very clever and very fast.
+	 * We simply lookup the phone in the fs_head list. We currently don't
+	 * open any additional phones (even though that itself would be pretty
+	 * straightforward; housekeeping multiple open phones to a FS task would
+	 * be more demanding). Instead, we simply take the respective
+	 * phone_futex and keep it until vfs_release_phone().
+	 */
+	futex_down(&fs_head_futex);
+	link_t *cur;
+	fs_info_t *fs;
+	for (cur = fs_head.next; cur != &fs_head; cur = cur->next) {
+		fs = list_get_instance(cur, fs_info_t, fs_link);
+		if (fs->fs_handle == handle) {
+			futex_up(&fs_head_futex);
+			/*
+			 * For now, take the futex unconditionally.
+			 * Oh yeah, serialization rocks.
+			 * It will be up'ed in vfs_release_phone().
+			 */
+			futex_down(&fs->phone_futex);
+			/*
+			 * Avoid deadlock with other fibrils in the same thread
+			 * by disabling fibril preemption.
+			 */
+			fibril_inc_sercount();
+			return fs->phone; 
+		}
+	}
+	futex_up(&fs_head_futex);
+	return 0;
+}
+
+/** Tell VFS that the phone is in use for any request.
+ *
+ * @param phone		Phone to FS task.
+ */
+void vfs_release_phone(int phone)
+{
+	bool found = false;
+
+	/*
+	 * Undo the fibril_inc_sercount() done in vfs_grab_phone().
+	 */
+	fibril_dec_sercount();
+	
+	futex_down(&fs_head_futex);
+	link_t *cur;
+	for (cur = fs_head.next; cur != &fs_head; cur = cur->next) {
+		fs_info_t *fs = list_get_instance(cur, fs_info_t, fs_link);
+		if (fs->phone == phone) {
+			found = true;
+			futex_up(&fs_head_futex);
+			futex_up(&fs->phone_futex);
+			return;
+		}
+	}
+	futex_up(&fs_head_futex);
+
+	/*
+	 * Not good to get here.
+	 */
+	assert(found == true);
+}
+
+/** Convert file system name to its handle.
+ *
+ * @param name		File system name.
+ * @param lock		If true, the function will down and up the
+ * 			fs_head_futex.
+ *
+ * @return		File system handle or zero if file system not found.
+ */
+int fs_name_to_handle(char *name, bool lock)
+{
+	int handle = 0;
+	
+	if (lock)
+		futex_down(&fs_head_futex);
+	link_t *cur;
+	for (cur = fs_head.next; cur != &fs_head; cur = cur->next) {
+		fs_info_t *fs = list_get_instance(cur, fs_info_t, fs_link);
+		if (strncmp(fs->vfs_info.name, name,
+		    sizeof(fs->vfs_info.name)) == 0) { 
+			handle = fs->fs_handle;
+			break;
+		}
+	}
+	if (lock)
+		futex_up(&fs_head_futex);
+	return handle;
+}
+
+/**
+ * @}
+ */ 
