Subversion Repositories HelenOS

/*

 * 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 structure where the lookup result will be stored.

 * @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_lookup_res_t *result,

    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->triplet.fs_handle = (int) IPC_GET_ARG1(answer);

		result->triplet.dev_handle = (int) IPC_GET_ARG2(answer);

		result->triplet.index = (int) IPC_GET_ARG3(answer);

		result->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_lookup_res_t *result)

{

	vfs_pair_t altroot = {

		.fs_handle = fs_handle,

		.dev_handle = dev_handle,

	};

	return vfs_lookup_internal("/", strlen("/"), result, &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_lookup_res_t mr_res;

	rc = lookup_root(fs_handle, dev_handle, &mr_res);

	if (rc != EOK) {

		free(buf);

		ipc_answer_0(rid, rc);

		return;

	}

	vfs_node_t *mr_node = vfs_node_get(&mr_res);

	if (!mr_node) {

		free(buf);

		ipc_answer_0(rid, ENOMEM);

		return;

	}

	/*

	 * Finally, we need to resolve the path to the mountpoint. 

	 */

	vfs_lookup_res_t mp_res;

	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_res, 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_res);

		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 = mr_res.triplet;

			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_res.triplet.fs_handle);

	/* Later we can use ARG3 to pass mode/flags. */

	aid_t req1 = async_send_3(phone, VFS_MOUNT,

	    (ipcarg_t) mp_res.triplet.dev_handle,

	    (ipcarg_t) mp_res.triplet.index, 0, NULL);

	/* The second call uses the same method. */

	aid_t req2 = async_send_3(phone, VFS_MOUNT,

	    (ipcarg_t) mr_res.triplet.fs_handle,

	    (ipcarg_t) mr_res.triplet.dev_handle,

	    (ipcarg_t) mr_res.triplet.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_lookup_res_t lr;

	rc = vfs_lookup_internal(path, len, &lr, 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(&lr);

	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_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_CLNT; 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;

}

/**

 * @}

 */