--- /dev/null
+Definitions
+~~~~~~~~~~~
+
+Userspace filesystem:
+
+ A filesystem in which data and metadata are provided by an ordinary
+ userspace process. The filesystem can be accessed normally through
+ the kernel interface.
+
+Filesystem daemon:
+
+ The process(es) providing the data and metadata of the filesystem.
+
+Non-privileged mount (or user mount):
+
+ A userspace filesystem mounted by a non-privileged (non-root) user.
+ The filesystem daemon is running with the privileges of the mounting
+ user. NOTE: this is not the same as mounts allowed with the "user"
+ option in /etc/fstab, which is not discussed here.
+
+Mount owner:
+
+ The user who does the mounting.
+
+User:
+
+ The user who is performing filesystem operations.
+
+What is FUSE?
+~~~~~~~~~~~~~
+
+FUSE is a userspace filesystem framework. It consists of a kernel
+module (fuse.ko), a userspace library (libfuse.*) and a mount utility
+(fusermount).
+
+One of the most important features of FUSE is allowing secure,
+non-privileged mounts. This opens up new possibilities for the use of
+filesystems. A good example is sshfs: a secure network filesystem
+using the sftp protocol.
+
+The userspace library and utilities are available from the FUSE
+homepage:
+
+ http://fuse.sourceforge.net/
+
+Mount options
+~~~~~~~~~~~~~
+
+'fd=N'
+
+ The file descriptor to use for communication between the userspace
+ filesystem and the kernel. The file descriptor must have been
+ obtained by opening the FUSE device ('/dev/fuse').
+
+'rootmode=M'
+
+ The file mode of the filesystem's root in octal representation.
+
+'user_id=N'
+
+ The numeric user id of the mount owner.
+
+'group_id=N'
+
+ The numeric group id of the mount owner.
+
+'default_permissions'
+
+ By default FUSE doesn't check file access permissions, the
+ filesystem is free to implement it's access policy or leave it to
+ the underlying file access mechanism (e.g. in case of network
+ filesystems). This option enables permission checking, restricting
+ access based on file mode. This is option is usually useful
+ together with the 'allow_other' mount option.
+
+'allow_other'
+
+ This option overrides the security measure restricting file access
+ to the user mounting the filesystem. This option is by default only
+ allowed to root, but this restriction can be removed with a
+ (userspace) configuration option.
+
+'kernel_cache'
+
+ This option disables flushing the cache of the file contents on
+ every open(). This should only be enabled on filesystems, where the
+ file data is never changed externally (not through the mounted FUSE
+ filesystem). Thus it is not suitable for network filesystems and
+ other "intermediate" filesystems.
+
+ NOTE: if this option is not specified (and neither 'direct_io') data
+ is still cached after the open(), so a read() system call will not
+ always initiate a read operation.
+
+'direct_io'
+
+ This option disables the use of page cache (file content cache) in
+ the kernel for this filesystem. This has several affects:
+
+ - Each read() or write() system call will initiate one or more
+ read or write operations, data will not be cached in the
+ kernel.
+
+ - The return value of the read() and write() system calls will
+ correspond to the return values of the read and write
+ operations. This is useful for example if the file size is not
+ known in advance (before reading it).
+
+'max_read=N'
+
+ With this option the maximum size of read operations can be set.
+ The default is infinite. Note that the size of read requests is
+ limited anyway to 32 pages (which is 128kbyte on i386).
+
+How do non-privileged mounts work?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Since the mount() system call is a privileged operation, a helper
+program (fusermount) is needed, which is installed setuid root.
+
+The implication of providing non-privileged mounts is that the mount
+owner must not be able to use this capability to compromise the
+system. Obvious requirements arising from this are:
+
+ A) mount owner should not be able to get elevated privileges with the
+ help of the mounted filesystem
+
+ B) mount owner should not get illegitimate access to information from
+ other users' and the super user's processes
+
+ C) mount owner should not be able to induce undesired behavior in
+ other users' or the super user's processes
+
+How are requirements fulfilled?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+ A) The mount owner could gain elevated privileges by either:
+
+ 1) creating a filesystem containing a device file, then opening
+ this device
+
+ 2) creating a filesystem containing a suid or sgid application,
+ then executing this application
+
+ The solution is not to allow opening device files and ignore
+ setuid and setgid bits when executing programs. To ensure this
+ fusermount always adds "nosuid" and "nodev" to the mount options
+ for non-privileged mounts.
+
+ B) If another user is accessing files or directories in the
+ filesystem, the filesystem daemon serving requests can record the
+ exact sequence and timing of operations performed. This
+ information is otherwise inaccessible to the mount owner, so this
+ counts as an information leak.
+
+ The solution to this problem will be presented in point 2) of C).
+
+ C) There are several ways in which the mount owner can induce
+ undesired behavior in other users' processes, such as:
+
+ 1) mounting a filesystem over a file or directory which the mount
+ owner could otherwise not be able to modify (or could only
+ make limited modifications).
+
+ This is solved in fusermount, by checking the access
+ permissions on the mountpoint and only allowing the mount if
+ the mount owner can do unlimited modification (has write
+ access to the mountpoint, and mountpoint is not a "sticky"
+ directory)
+
+ 2) Even if 1) is solved the mount owner can change the behavior
+ of other users' processes.
+
+ i) It can slow down or indefinitely delay the execution of a
+ filesystem operation creating a DoS against the user or the
+ whole system. For example a suid application locking a
+ system file, and then accessing a file on the mount owner's
+ filesystem could be stopped, and thus causing the system
+ file to be locked forever.
+
+ ii) It can present files or directories of unlimited length, or
+ directory structures of unlimited depth, possibly causing a
+ system process to eat up diskspace, memory or other
+ resources, again causing DoS.
+
+ The solution to this as well as B) is not to allow processes
+ to access the filesystem, which could otherwise not be
+ monitored or manipulated by the mount owner. Since if the
+ mount owner can ptrace a process, it can do all of the above
+ without using a FUSE mount, the same criteria as used in
+ ptrace can be used to check if a process is allowed to access
+ the filesystem or not.
+
+ Note that the ptrace check is not strictly necessary to
+ prevent B/2/i, it is enough to check if mount owner has enough
+ privilege to send signal to the process accessing the
+ filesystem, since SIGSTOP can be used to get a similar effect.
+
+I think these limitations are unacceptable?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If a sysadmin trusts the users enough, or can ensure through other
+measures, that system processes will never enter non-privileged
+mounts, it can relax the last limitation with a "user_allow_other"
+config option. If this config option is set, the mounting user can
+add the "allow_other" mount option which disables the check for other
+users' processes.
+
+Kernel - userspace interface
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following diagram shows how a filesystem operation (in this
+example unlink) is performed in FUSE.
+
+NOTE: everything in this description is greatly simplified
+
+ | "rm /mnt/fuse/file" | FUSE filesystem daemon
+ | |
+ | | >sys_read()
+ | | >fuse_dev_read()
+ | | >request_wait()
+ | | [sleep on fc->waitq]
+ | |
+ | >sys_unlink() |
+ | >fuse_unlink() |
+ | [get request from |
+ | fc->unused_list] |
+ | >request_send() |
+ | [queue req on fc->pending] |
+ | [wake up fc->waitq] | [woken up]
+ | >request_wait_answer() |
+ | [sleep on req->waitq] |
+ | | <request_wait()
+ | | [remove req from fc->pending]
+ | | [copy req to read buffer]
+ | | [add req to fc->processing]
+ | | <fuse_dev_read()
+ | | <sys_read()
+ | |
+ | | [perform unlink]
+ | |
+ | | >sys_write()
+ | | >fuse_dev_write()
+ | | [look up req in fc->processing]
+ | | [remove from fc->processing]
+ | | [copy write buffer to req]
+ | [woken up] | [wake up req->waitq]
+ | | <fuse_dev_write()
+ | | <sys_write()
+ | <request_wait_answer() |
+ | <request_send() |
+ | [add request to |
+ | fc->unused_list] |
+ | <fuse_unlink() |
+ | <sys_unlink() |
+
+There are a couple of ways in which to deadlock a FUSE filesystem.
+Since we are talking about unprivileged userspace programs,
+something must be done about these.
+
+Scenario 1 - Simple deadlock
+-----------------------------
+
+ | "rm /mnt/fuse/file" | FUSE filesystem daemon
+ | |
+ | >sys_unlink("/mnt/fuse/file") |
+ | [acquire inode semaphore |
+ | for "file"] |
+ | >fuse_unlink() |
+ | [sleep on req->waitq] |
+ | | <sys_read()
+ | | >sys_unlink("/mnt/fuse/file")
+ | | [acquire inode semaphore
+ | | for "file"]
+ | | *DEADLOCK*
+
+The solution for this is to allow requests to be interrupted while
+they are in userspace:
+
+ | [interrupted by signal] |
+ | <fuse_unlink() |
+ | [release semaphore] | [semaphore acquired]
+ | <sys_unlink() |
+ | | >fuse_unlink()
+ | | [queue req on fc->pending]
+ | | [wake up fc->waitq]
+ | | [sleep on req->waitq]
+
+If the filesystem daemon was single threaded, this will stop here,
+since there's no other thread to dequeue and execute the request.
+In this case the solution is to kill the FUSE daemon as well. If
+there are multiple serving threads, you just have to kill them as
+long as any remain.
+
+Moral: a filesystem which deadlocks, can soon find itself dead.
+
+Scenario 2 - Tricky deadlock
+----------------------------
+
+This one needs a carefully crafted filesystem. It's a variation on
+the above, only the call back to the filesystem is not explicit,
+but is caused by a pagefault.
+
+ | Kamikaze filesystem thread 1 | Kamikaze filesystem thread 2
+ | |
+ | [fd = open("/mnt/fuse/file")] | [request served normally]
+ | [mmap fd to 'addr'] |
+ | [close fd] | [FLUSH triggers 'magic' flag]
+ | [read a byte from addr] |
+ | >do_page_fault() |
+ | [find or create page] |
+ | [lock page] |
+ | >fuse_readpage() |
+ | [queue READ request] |
+ | [sleep on req->waitq] |
+ | | [read request to buffer]
+ | | [create reply header before addr]
+ | | >sys_write(addr - headerlength)
+ | | >fuse_dev_write()
+ | | [look up req in fc->processing]
+ | | [remove from fc->processing]
+ | | [copy write buffer to req]
+ | | >do_page_fault()
+ | | [find or create page]
+ | | [lock page]
+ | | * DEADLOCK *
+
+Solution is again to let the the request be interrupted (not
+elaborated further).
+
+An additional problem is that while the write buffer is being
+copied to the request, the request must not be interrupted. This
+is because the destination address of the copy may not be valid
+after the request is interrupted.
+
+This is solved with doing the copy atomically, and allowing
+interruption while the page(s) belonging to the write buffer are
+faulted with get_user_pages(). The 'req->locked' flag indicates
+when the copy is taking place, and interruption is delayed until
+this flag is unset.
+
--- /dev/null
+/*
+ FUSE: Filesystem in Userspace
+ Copyright (C) 2001-2005 Miklos Szeredi <miklos@szeredi.hu>
+
+ This program can be distributed under the terms of the GNU GPL.
+ See the file COPYING.
+*/
+
+#include "fuse_i.h"
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+#include <linux/uio.h>
+#include <linux/miscdevice.h>
+#include <linux/pagemap.h>
+#include <linux/file.h>
+#include <linux/slab.h>
+
+MODULE_ALIAS_MISCDEV(FUSE_MINOR);
+
+static kmem_cache_t *fuse_req_cachep;
+
+static inline struct fuse_conn *fuse_get_conn(struct file *file)
+{
+ struct fuse_conn *fc;
+ spin_lock(&fuse_lock);
+ fc = file->private_data;
+ if (fc && !fc->sb)
+ fc = NULL;
+ spin_unlock(&fuse_lock);
+ return fc;
+}
+
+static inline void fuse_request_init(struct fuse_req *req)
+{
+ memset(req, 0, sizeof(*req));
+ INIT_LIST_HEAD(&req->list);
+ init_waitqueue_head(&req->waitq);
+ atomic_set(&req->count, 1);
+}
+
+struct fuse_req *fuse_request_alloc(void)
+{
+ struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, SLAB_KERNEL);
+ if (req)
+ fuse_request_init(req);
+ return req;
+}
+
+void fuse_request_free(struct fuse_req *req)
+{
+ kmem_cache_free(fuse_req_cachep, req);
+}
+
+static inline void block_sigs(sigset_t *oldset)
+{
+ sigset_t mask;
+
+ siginitsetinv(&mask, sigmask(SIGKILL));
+ sigprocmask(SIG_BLOCK, &mask, oldset);
+}
+
+static inline void restore_sigs(sigset_t *oldset)
+{
+ sigprocmask(SIG_SETMASK, oldset, NULL);
+}
+
+void fuse_reset_request(struct fuse_req *req)
+{
+ int preallocated = req->preallocated;
+ BUG_ON(atomic_read(&req->count) != 1);
+ fuse_request_init(req);
+ req->preallocated = preallocated;
+}
+
+static void __fuse_get_request(struct fuse_req *req)
+{
+ atomic_inc(&req->count);
+}
+
+/* Must be called with > 1 refcount */
+static void __fuse_put_request(struct fuse_req *req)
+{
+ BUG_ON(atomic_read(&req->count) < 2);
+ atomic_dec(&req->count);
+}
+
+static struct fuse_req *do_get_request(struct fuse_conn *fc)
+{
+ struct fuse_req *req;
+
+ spin_lock(&fuse_lock);
+ BUG_ON(list_empty(&fc->unused_list));
+ req = list_entry(fc->unused_list.next, struct fuse_req, list);
+ list_del_init(&req->list);
+ spin_unlock(&fuse_lock);
+ fuse_request_init(req);
+ req->preallocated = 1;
+ req->in.h.uid = current->fsuid;
+ req->in.h.gid = current->fsgid;
+ req->in.h.pid = current->pid;
+ return req;
+}
+
+struct fuse_req *fuse_get_request(struct fuse_conn *fc)
+{
+ if (down_interruptible(&fc->outstanding_sem))
+ return NULL;
+ return do_get_request(fc);
+}
+
+/*
+ * Non-interruptible version of the above function is for operations
+ * which can't legally return -ERESTART{SYS,NOINTR}. This can still
+ * return NULL, but only in case the signal is SIGKILL.
+ */
+struct fuse_req *fuse_get_request_nonint(struct fuse_conn *fc)
+{
+ int intr;
+ sigset_t oldset;
+
+ block_sigs(&oldset);
+ intr = down_interruptible(&fc->outstanding_sem);
+ restore_sigs(&oldset);
+ return intr ? NULL : do_get_request(fc);
+}
+
+static void fuse_putback_request(struct fuse_conn *fc, struct fuse_req *req)
+{
+ spin_lock(&fuse_lock);
+ if (req->preallocated)
+ list_add(&req->list, &fc->unused_list);
+ else
+ fuse_request_free(req);
+
+ /* If we are in debt decrease that first */
+ if (fc->outstanding_debt)
+ fc->outstanding_debt--;
+ else
+ up(&fc->outstanding_sem);
+ spin_unlock(&fuse_lock);
+}
+
+void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
+{
+ if (atomic_dec_and_test(&req->count))
+ fuse_putback_request(fc, req);
+}
+
+/*
+ * This function is called when a request is finished. Either a reply
+ * has arrived or it was interrupted (and not yet sent) or some error
+ * occured during communication with userspace, or the device file was
+ * closed. It decreases the referece count for the request. In case
+ * of a background request the referece to the stored objects are
+ * released. The requester thread is woken up (if still waiting), and
+ * finally the request is either freed or put on the unused_list
+ *
+ * Called with fuse_lock, unlocks it
+ */
+static void request_end(struct fuse_conn *fc, struct fuse_req *req)
+{
+ int putback;
+ req->finished = 1;
+ putback = atomic_dec_and_test(&req->count);
+ spin_unlock(&fuse_lock);
+ if (req->background) {
+ if (req->inode)
+ iput(req->inode);
+ if (req->inode2)
+ iput(req->inode2);
+ if (req->file)
+ fput(req->file);
+ }
+ wake_up(&req->waitq);
+ if (req->in.h.opcode == FUSE_INIT) {
+ int i;
+
+ if (req->misc.init_in_out.major != FUSE_KERNEL_VERSION)
+ fc->conn_error = 1;
+
+ /* After INIT reply is received other requests can go
+ out. So do (FUSE_MAX_OUTSTANDING - 1) number of
+ up()s on outstanding_sem. The last up() is done in
+ fuse_putback_request() */
+ for (i = 1; i < FUSE_MAX_OUTSTANDING; i++)
+ up(&fc->outstanding_sem);
+ }
+ if (putback)
+ fuse_putback_request(fc, req);
+}
+
+static void background_request(struct fuse_req *req)
+{
+ /* Need to get hold of the inode(s) and/or file used in the
+ request, so FORGET and RELEASE are not sent too early */
+ req->background = 1;
+ if (req->inode)
+ req->inode = igrab(req->inode);
+ if (req->inode2)
+ req->inode2 = igrab(req->inode2);
+ if (req->file)
+ get_file(req->file);
+}
+
+static int request_wait_answer_nonint(struct fuse_req *req)
+{
+ int err;
+ sigset_t oldset;
+ block_sigs(&oldset);
+ err = wait_event_interruptible(req->waitq, req->finished);
+ restore_sigs(&oldset);
+ return err;
+}
+
+/* Called with fuse_lock held. Releases, and then reacquires it. */
+static void request_wait_answer(struct fuse_req *req, int interruptible)
+{
+ int intr;
+
+ spin_unlock(&fuse_lock);
+ if (interruptible)
+ intr = wait_event_interruptible(req->waitq, req->finished);
+ else
+ intr = request_wait_answer_nonint(req);
+ spin_lock(&fuse_lock);
+ if (intr && interruptible && req->sent) {
+ /* If request is already in userspace, only allow KILL
+ signal to interrupt */
+ spin_unlock(&fuse_lock);
+ intr = request_wait_answer_nonint(req);
+ spin_lock(&fuse_lock);
+ }
+ if (!intr)
+ return;
+
+ if (!interruptible || req->sent)
+ req->out.h.error = -EINTR;
+ else
+ req->out.h.error = -ERESTARTNOINTR;
+
+ req->interrupted = 1;
+ if (req->locked) {
+ /* This is uninterruptible sleep, because data is
+ being copied to/from the buffers of req. During
+ locked state, there mustn't be any filesystem
+ operation (e.g. page fault), since that could lead
+ to deadlock */
+ spin_unlock(&fuse_lock);
+ wait_event(req->waitq, !req->locked);
+ spin_lock(&fuse_lock);
+ }
+ if (!req->sent && !list_empty(&req->list)) {
+ list_del(&req->list);
+ __fuse_put_request(req);
+ } else if (!req->finished && req->sent)
+ background_request(req);
+}
+
+static unsigned len_args(unsigned numargs, struct fuse_arg *args)
+{
+ unsigned nbytes = 0;
+ unsigned i;
+
+ for (i = 0; i < numargs; i++)
+ nbytes += args[i].size;
+
+ return nbytes;
+}
+
+static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
+{
+ fc->reqctr++;
+ /* zero is special */
+ if (fc->reqctr == 0)
+ fc->reqctr = 1;
+ req->in.h.unique = fc->reqctr;
+ req->in.h.len = sizeof(struct fuse_in_header) +
+ len_args(req->in.numargs, (struct fuse_arg *) req->in.args);
+ if (!req->preallocated) {
+ /* If request is not preallocated (either FORGET or
+ RELEASE), then still decrease outstanding_sem, so
+ user can't open infinite number of files while not
+ processing the RELEASE requests. However for
+ efficiency do it without blocking, so if down()
+ would block, just increase the debt instead */
+ if (down_trylock(&fc->outstanding_sem))
+ fc->outstanding_debt++;
+ }
+ list_add_tail(&req->list, &fc->pending);
+ wake_up(&fc->waitq);
+}
+
+static void request_send_wait(struct fuse_conn *fc, struct fuse_req *req,
+ int interruptible)
+{
+ req->isreply = 1;
+ spin_lock(&fuse_lock);
+ if (!fc->file)
+ req->out.h.error = -ENOTCONN;
+ else if (fc->conn_error)
+ req->out.h.error = -ECONNREFUSED;
+ else {
+ queue_request(fc, req);
+ /* acquire extra reference, since request is still needed
+ after request_end() */
+ __fuse_get_request(req);
+
+ request_wait_answer(req, interruptible);
+ }
+ spin_unlock(&fuse_lock);
+}
+
+void request_send(struct fuse_conn *fc, struct fuse_req *req)
+{
+ request_send_wait(fc, req, 1);
+}
+
+/*
+ * Non-interruptible version of the above function is for operations
+ * which can't legally return -ERESTART{SYS,NOINTR}. This can still
+ * be interrupted but only with SIGKILL.
+ */
+void request_send_nonint(struct fuse_conn *fc, struct fuse_req *req)
+{
+ request_send_wait(fc, req, 0);
+}
+
+static void request_send_nowait(struct fuse_conn *fc, struct fuse_req *req)
+{
+ spin_lock(&fuse_lock);
+ if (fc->file) {
+ queue_request(fc, req);
+ spin_unlock(&fuse_lock);
+ } else {
+ req->out.h.error = -ENOTCONN;
+ request_end(fc, req);
+ }
+}
+
+void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req)
+{
+ req->isreply = 0;
+ request_send_nowait(fc, req);
+}
+
+void request_send_background(struct fuse_conn *fc, struct fuse_req *req)
+{
+ req->isreply = 1;
+ background_request(req);
+ request_send_nowait(fc, req);
+}
+
+void fuse_send_init(struct fuse_conn *fc)
+{
+ /* This is called from fuse_read_super() so there's guaranteed
+ to be a request available */
+ struct fuse_req *req = do_get_request(fc);
+ struct fuse_init_in_out *arg = &req->misc.init_in_out;
+ arg->major = FUSE_KERNEL_VERSION;
+ arg->minor = FUSE_KERNEL_MINOR_VERSION;
+ req->in.h.opcode = FUSE_INIT;
+ req->in.numargs = 1;
+ req->in.args[0].size = sizeof(*arg);
+ req->in.args[0].value = arg;
+ req->out.numargs = 1;
+ req->out.args[0].size = sizeof(*arg);
+ req->out.args[0].value = arg;
+ request_send_background(fc, req);
+}
+
+/*
+ * Lock the request. Up to the next unlock_request() there mustn't be
+ * anything that could cause a page-fault. If the request was already
+ * interrupted bail out.
+ */
+static inline int lock_request(struct fuse_req *req)
+{
+ int err = 0;
+ if (req) {
+ spin_lock(&fuse_lock);
+ if (req->interrupted)
+ err = -ENOENT;
+ else
+ req->locked = 1;
+ spin_unlock(&fuse_lock);
+ }
+ return err;
+}
+
+/*
+ * Unlock request. If it was interrupted during being locked, the
+ * requester thread is currently waiting for it to be unlocked, so
+ * wake it up.
+ */
+static inline void unlock_request(struct fuse_req *req)
+{
+ if (req) {
+ spin_lock(&fuse_lock);
+ req->locked = 0;
+ if (req->interrupted)
+ wake_up(&req->waitq);
+ spin_unlock(&fuse_lock);
+ }
+}
+
+struct fuse_copy_state {
+ int write;
+ struct fuse_req *req;
+ const struct iovec *iov;
+ unsigned long nr_segs;
+ unsigned long seglen;
+ unsigned long addr;
+ struct page *pg;
+ void *mapaddr;
+ void *buf;
+ unsigned len;
+};
+
+static void fuse_copy_init(struct fuse_copy_state *cs, int write,
+ struct fuse_req *req, const struct iovec *iov,
+ unsigned long nr_segs)
+{
+ memset(cs, 0, sizeof(*cs));
+ cs->write = write;
+ cs->req = req;
+ cs->iov = iov;
+ cs->nr_segs = nr_segs;
+}
+
+/* Unmap and put previous page of userspace buffer */
+static inline void fuse_copy_finish(struct fuse_copy_state *cs)
+{
+ if (cs->mapaddr) {
+ kunmap_atomic(cs->mapaddr, KM_USER0);
+ if (cs->write) {
+ flush_dcache_page(cs->pg);
+ set_page_dirty_lock(cs->pg);
+ }
+ put_page(cs->pg);
+ cs->mapaddr = NULL;
+ }
+}
+
+/*
+ * Get another pagefull of userspace buffer, and map it to kernel
+ * address space, and lock request
+ */
+static int fuse_copy_fill(struct fuse_copy_state *cs)
+{
+ unsigned long offset;
+ int err;
+
+ unlock_request(cs->req);
+ fuse_copy_finish(cs);
+ if (!cs->seglen) {
+ BUG_ON(!cs->nr_segs);
+ cs->seglen = cs->iov[0].iov_len;
+ cs->addr = (unsigned long) cs->iov[0].iov_base;
+ cs->iov ++;
+ cs->nr_segs --;
+ }
+ down_read(¤t->mm->mmap_sem);
+ err = get_user_pages(current, current->mm, cs->addr, 1, cs->write, 0,
+ &cs->pg, NULL);
+ up_read(¤t->mm->mmap_sem);
+ if (err < 0)
+ return err;
+ BUG_ON(err != 1);
+ offset = cs->addr % PAGE_SIZE;
+ cs->mapaddr = kmap_atomic(cs->pg, KM_USER0);
+ cs->buf = cs->mapaddr + offset;
+ cs->len = min(PAGE_SIZE - offset, cs->seglen);
+ cs->seglen -= cs->len;
+ cs->addr += cs->len;
+
+ return lock_request(cs->req);
+}
+
+/* Do as much copy to/from userspace buffer as we can */
+static inline int fuse_copy_do(struct fuse_copy_state *cs, void **val,
+ unsigned *size)
+{
+ unsigned ncpy = min(*size, cs->len);
+ if (val) {
+ if (cs->write)
+ memcpy(cs->buf, *val, ncpy);
+ else
+ memcpy(*val, cs->buf, ncpy);
+ *val += ncpy;
+ }
+ *size -= ncpy;
+ cs->len -= ncpy;
+ cs->buf += ncpy;
+ return ncpy;
+}
+
+/*
+ * Copy a page in the request to/from the userspace buffer. Must be
+ * done atomically
+ */
+static inline int fuse_copy_page(struct fuse_copy_state *cs, struct page *page,
+ unsigned offset, unsigned count, int zeroing)
+{
+ if (page && zeroing && count < PAGE_SIZE) {
+ void *mapaddr = kmap_atomic(page, KM_USER1);
+ memset(mapaddr, 0, PAGE_SIZE);
+ kunmap_atomic(mapaddr, KM_USER1);
+ }
+ while (count) {
+ int err;
+ if (!cs->len && (err = fuse_copy_fill(cs)))
+ return err;
+ if (page) {
+ void *mapaddr = kmap_atomic(page, KM_USER1);
+ void *buf = mapaddr + offset;
+ offset += fuse_copy_do(cs, &buf, &count);
+ kunmap_atomic(mapaddr, KM_USER1);
+ } else
+ offset += fuse_copy_do(cs, NULL, &count);
+ }
+ if (page && !cs->write)
+ flush_dcache_page(page);
+ return 0;
+}
+
+/* Copy pages in the request to/from userspace buffer */
+static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
+ int zeroing)
+{
+ unsigned i;
+ struct fuse_req *req = cs->req;
+ unsigned offset = req->page_offset;
+ unsigned count = min(nbytes, (unsigned) PAGE_SIZE - offset);
+
+ for (i = 0; i < req->num_pages && (nbytes || zeroing); i++) {
+ struct page *page = req->pages[i];
+ int err = fuse_copy_page(cs, page, offset, count, zeroing);
+ if (err)
+ return err;
+
+ nbytes -= count;
+ count = min(nbytes, (unsigned) PAGE_SIZE);
+ offset = 0;
+ }
+ return 0;
+}
+
+/* Copy a single argument in the request to/from userspace buffer */
+static int fuse_copy_one(struct fuse_copy_state *cs, void *val, unsigned size)
+{
+ while (size) {
+ int err;
+ if (!cs->len && (err = fuse_copy_fill(cs)))
+ return err;
+ fuse_copy_do(cs, &val, &size);
+ }
+ return 0;
+}
+
+/* Copy request arguments to/from userspace buffer */
+static int fuse_copy_args(struct fuse_copy_state *cs, unsigned numargs,
+ unsigned argpages, struct fuse_arg *args,
+ int zeroing)
+{
+ int err = 0;
+ unsigned i;
+
+ for (i = 0; !err && i < numargs; i++) {
+ struct fuse_arg *arg = &args[i];
+ if (i == numargs - 1 && argpages)
+ err = fuse_copy_pages(cs, arg->size, zeroing);
+ else
+ err = fuse_copy_one(cs, arg->value, arg->size);
+ }
+ return err;
+}
+
+/* Wait until a request is available on the pending list */
+static void request_wait(struct fuse_conn *fc)
+{
+ DECLARE_WAITQUEUE(wait, current);
+
+ add_wait_queue_exclusive(&fc->waitq, &wait);
+ while (fc->sb && list_empty(&fc->pending)) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (signal_pending(current))
+ break;
+
+ spin_unlock(&fuse_lock);
+ schedule();
+ spin_lock(&fuse_lock);
+ }
+ set_current_state(TASK_RUNNING);
+ remove_wait_queue(&fc->waitq, &wait);
+}
+
+/*
+ * Read a single request into the userspace filesystem's buffer. This
+ * function waits until a request is available, then removes it from
+ * the pending list and copies request data to userspace buffer. If
+ * no reply is needed (FORGET) or request has been interrupted or
+ * there was an error during the copying then it's finished by calling
+ * request_end(). Otherwise add it to the processing list, and set
+ * the 'sent' flag.
+ */
+static ssize_t fuse_dev_readv(struct file *file, const struct iovec *iov,
+ unsigned long nr_segs, loff_t *off)
+{
+ int err;
+ struct fuse_conn *fc;
+ struct fuse_req *req;
+ struct fuse_in *in;
+ struct fuse_copy_state cs;
+ unsigned reqsize;
+
+ spin_lock(&fuse_lock);
+ fc = file->private_data;
+ err = -EPERM;
+ if (!fc)
+ goto err_unlock;
+ request_wait(fc);
+ err = -ENODEV;
+ if (!fc->sb)
+ goto err_unlock;
+ err = -ERESTARTSYS;
+ if (list_empty(&fc->pending))
+ goto err_unlock;
+
+ req = list_entry(fc->pending.next, struct fuse_req, list);
+ list_del_init(&req->list);
+ spin_unlock(&fuse_lock);
+
+ in = &req->in;
+ reqsize = req->in.h.len;
+ fuse_copy_init(&cs, 1, req, iov, nr_segs);
+ err = -EINVAL;
+ if (iov_length(iov, nr_segs) >= reqsize) {
+ err = fuse_copy_one(&cs, &in->h, sizeof(in->h));
+ if (!err)
+ err = fuse_copy_args(&cs, in->numargs, in->argpages,
+ (struct fuse_arg *) in->args, 0);
+ }
+ fuse_copy_finish(&cs);
+
+ spin_lock(&fuse_lock);
+ req->locked = 0;
+ if (!err && req->interrupted)
+ err = -ENOENT;
+ if (err) {
+ if (!req->interrupted)
+ req->out.h.error = -EIO;
+ request_end(fc, req);
+ return err;
+ }
+ if (!req->isreply)
+ request_end(fc, req);
+ else {
+ req->sent = 1;
+ list_add_tail(&req->list, &fc->processing);
+ spin_unlock(&fuse_lock);
+ }
+ return reqsize;
+
+ err_unlock:
+ spin_unlock(&fuse_lock);
+ return err;
+}
+
+static ssize_t fuse_dev_read(struct file *file, char __user *buf,
+ size_t nbytes, loff_t *off)
+{
+ struct iovec iov;
+ iov.iov_len = nbytes;
+ iov.iov_base = buf;
+ return fuse_dev_readv(file, &iov, 1, off);
+}
+
+/* Look up request on processing list by unique ID */
+static struct fuse_req *request_find(struct fuse_conn *fc, u64 unique)
+{
+ struct list_head *entry;
+
+ list_for_each(entry, &fc->processing) {
+ struct fuse_req *req;
+ req = list_entry(entry, struct fuse_req, list);
+ if (req->in.h.unique == unique)
+ return req;
+ }
+ return NULL;
+}
+
+static int copy_out_args(struct fuse_copy_state *cs, struct fuse_out *out,
+ unsigned nbytes)
+{
+ unsigned reqsize = sizeof(struct fuse_out_header);
+
+ if (out->h.error)
+ return nbytes != reqsize ? -EINVAL : 0;
+
+ reqsize += len_args(out->numargs, out->args);
+
+ if (reqsize < nbytes || (reqsize > nbytes && !out->argvar))
+ return -EINVAL;
+ else if (reqsize > nbytes) {
+ struct fuse_arg *lastarg = &out->args[out->numargs-1];
+ unsigned diffsize = reqsize - nbytes;
+ if (diffsize > lastarg->size)
+ return -EINVAL;
+ lastarg->size -= diffsize;
+ }
+ return fuse_copy_args(cs, out->numargs, out->argpages, out->args,
+ out->page_zeroing);
+}
+
+/*
+ * Write a single reply to a request. First the header is copied from
+ * the write buffer. The request is then searched on the processing
+ * list by the unique ID found in the header. If found, then remove
+ * it from the list and copy the rest of the buffer to the request.
+ * The request is finished by calling request_end()
+ */
+static ssize_t fuse_dev_writev(struct file *file, const struct iovec *iov,
+ unsigned long nr_segs, loff_t *off)
+{
+ int err;
+ unsigned nbytes = iov_length(iov, nr_segs);
+ struct fuse_req *req;
+ struct fuse_out_header oh;
+ struct fuse_copy_state cs;
+ struct fuse_conn *fc = fuse_get_conn(file);
+ if (!fc)
+ return -ENODEV;
+
+ fuse_copy_init(&cs, 0, NULL, iov, nr_segs);
+ if (nbytes < sizeof(struct fuse_out_header))
+ return -EINVAL;
+
+ err = fuse_copy_one(&cs, &oh, sizeof(oh));
+ if (err)
+ goto err_finish;
+ err = -EINVAL;
+ if (!oh.unique || oh.error <= -1000 || oh.error > 0 ||
+ oh.len != nbytes)
+ goto err_finish;
+
+ spin_lock(&fuse_lock);
+ req = request_find(fc, oh.unique);
+ err = -EINVAL;
+ if (!req)
+ goto err_unlock;
+
+ list_del_init(&req->list);
+ if (req->interrupted) {
+ request_end(fc, req);
+ fuse_copy_finish(&cs);
+ return -ENOENT;
+ }
+ req->out.h = oh;
+ req->locked = 1;
+ cs.req = req;
+ spin_unlock(&fuse_lock);
+
+ err = copy_out_args(&cs, &req->out, nbytes);
+ fuse_copy_finish(&cs);
+
+ spin_lock(&fuse_lock);
+ req->locked = 0;
+ if (!err) {
+ if (req->interrupted)
+ err = -ENOENT;
+ } else if (!req->interrupted)
+ req->out.h.error = -EIO;
+ request_end(fc, req);
+
+ return err ? err : nbytes;
+
+ err_unlock:
+ spin_unlock(&fuse_lock);
+ err_finish:
+ fuse_copy_finish(&cs);
+ return err;
+}
+
+static ssize_t fuse_dev_write(struct file *file, const char __user *buf,
+ size_t nbytes, loff_t *off)
+{
+ struct iovec iov;
+ iov.iov_len = nbytes;
+ iov.iov_base = (char __user *) buf;
+ return fuse_dev_writev(file, &iov, 1, off);
+}
+
+static unsigned fuse_dev_poll(struct file *file, poll_table *wait)
+{
+ struct fuse_conn *fc = fuse_get_conn(file);
+ unsigned mask = POLLOUT | POLLWRNORM;
+
+ if (!fc)
+ return -ENODEV;
+
+ poll_wait(file, &fc->waitq, wait);
+
+ spin_lock(&fuse_lock);
+ if (!list_empty(&fc->pending))
+ mask |= POLLIN | POLLRDNORM;
+ spin_unlock(&fuse_lock);
+
+ return mask;
+}
+
+/* Abort all requests on the given list (pending or processing) */
+static void end_requests(struct fuse_conn *fc, struct list_head *head)
+{
+ while (!list_empty(head)) {
+ struct fuse_req *req;
+ req = list_entry(head->next, struct fuse_req, list);
+ list_del_init(&req->list);
+ req->out.h.error = -ECONNABORTED;
+ request_end(fc, req);
+ spin_lock(&fuse_lock);
+ }
+}
+
+static int fuse_dev_release(struct inode *inode, struct file *file)
+{
+ struct fuse_conn *fc;
+
+ spin_lock(&fuse_lock);
+ fc = file->private_data;
+ if (fc) {
+ fc->file = NULL;
+ end_requests(fc, &fc->pending);
+ end_requests(fc, &fc->processing);
+ fuse_release_conn(fc);
+ }
+ spin_unlock(&fuse_lock);
+ return 0;
+}
+
+struct file_operations fuse_dev_operations = {
+ .owner = THIS_MODULE,
+ .llseek = no_llseek,
+ .read = fuse_dev_read,
+ .readv = fuse_dev_readv,
+ .write = fuse_dev_write,
+ .writev = fuse_dev_writev,
+ .poll = fuse_dev_poll,
+ .release = fuse_dev_release,
+};
+
+static struct miscdevice fuse_miscdevice = {
+ .minor = FUSE_MINOR,
+ .name = "fuse",
+ .fops = &fuse_dev_operations,
+};
+
+int __init fuse_dev_init(void)
+{
+ int err = -ENOMEM;
+ fuse_req_cachep = kmem_cache_create("fuse_request",
+ sizeof(struct fuse_req),
+ 0, 0, NULL, NULL);
+ if (!fuse_req_cachep)
+ goto out;
+
+ err = misc_register(&fuse_miscdevice);
+ if (err)
+ goto out_cache_clean;
+
+ return 0;
+
+ out_cache_clean:
+ kmem_cache_destroy(fuse_req_cachep);
+ out:
+ return err;
+}
+
+void fuse_dev_cleanup(void)
+{
+ misc_deregister(&fuse_miscdevice);
+ kmem_cache_destroy(fuse_req_cachep);
+}
#include <linux/backing-dev.h>
#include <asm/semaphore.h>
+/** Max number of pages that can be used in a single read request */
+#define FUSE_MAX_PAGES_PER_REQ 32
+
+/** If more requests are outstanding, then the operation will block */
+#define FUSE_MAX_OUTSTANDING 10
+
/** FUSE inode */
struct fuse_inode {
/** Inode data */
unsigned long i_time;
};
+/** One input argument of a request */
+struct fuse_in_arg {
+ unsigned size;
+ const void *value;
+};
+
+/** The request input */
+struct fuse_in {
+ /** The request header */
+ struct fuse_in_header h;
+
+ /** True if the data for the last argument is in req->pages */
+ unsigned argpages:1;
+
+ /** Number of arguments */
+ unsigned numargs;
+
+ /** Array of arguments */
+ struct fuse_in_arg args[3];
+};
+
+/** One output argument of a request */
+struct fuse_arg {
+ unsigned size;
+ void *value;
+};
+
+/** The request output */
+struct fuse_out {
+ /** Header returned from userspace */
+ struct fuse_out_header h;
+
+ /** Last argument is variable length (can be shorter than
+ arg->size) */
+ unsigned argvar:1;
+
+ /** Last argument is a list of pages to copy data to */
+ unsigned argpages:1;
+
+ /** Zero partially or not copied pages */
+ unsigned page_zeroing:1;
+
+ /** Number or arguments */
+ unsigned numargs;
+
+ /** Array of arguments */
+ struct fuse_arg args[3];
+};
+
+struct fuse_req;
+struct fuse_conn;
+
+/**
+ * A request to the client
+ */
+struct fuse_req {
+ /** This can be on either unused_list, pending or processing
+ lists in fuse_conn */
+ struct list_head list;
+
+ /** refcount */
+ atomic_t count;
+
+ /** True if the request has reply */
+ unsigned isreply:1;
+
+ /** The request is preallocated */
+ unsigned preallocated:1;
+
+ /** The request was interrupted */
+ unsigned interrupted:1;
+
+ /** Request is sent in the background */
+ unsigned background:1;
+
+ /** Data is being copied to/from the request */
+ unsigned locked:1;
+
+ /** Request has been sent to userspace */
+ unsigned sent:1;
+
+ /** The request is finished */
+ unsigned finished:1;
+
+ /** The request input */
+ struct fuse_in in;
+
+ /** The request output */
+ struct fuse_out out;
+
+ /** Used to wake up the task waiting for completion of request*/
+ wait_queue_head_t waitq;
+
+ /** Data for asynchronous requests */
+ union {
+ struct fuse_init_in_out init_in_out;
+ } misc;
+
+ /** page vector */
+ struct page *pages[FUSE_MAX_PAGES_PER_REQ];
+
+ /** number of pages in vector */
+ unsigned num_pages;
+
+ /** offset of data on first page */
+ unsigned page_offset;
+
+ /** Inode used in the request */
+ struct inode *inode;
+
+ /** Second inode used in the request (or NULL) */
+ struct inode *inode2;
+
+ /** File used in the request (or NULL) */
+ struct file *file;
+};
+
/**
* A Fuse connection.
*
/** The superblock of the mounted filesystem */
struct super_block *sb;
+ /** The opened client device */
+ struct file *file;
+
/** The user id for this mount */
uid_t user_id;
+ /** Readers of the connection are waiting on this */
+ wait_queue_head_t waitq;
+
+ /** The list of pending requests */
+ struct list_head pending;
+
+ /** The list of requests being processed */
+ struct list_head processing;
+
+ /** Controls the maximum number of outstanding requests */
+ struct semaphore outstanding_sem;
+
+ /** This counts the number of outstanding requests if
+ outstanding_sem would go negative */
+ unsigned outstanding_debt;
+
+ /** The list of unused requests */
+ struct list_head unused_list;
+
+ /** The next unique request id */
+ u64 reqctr;
+
+ /** Connection failed (version mismatch) */
+ unsigned conn_error : 1;
+
/** Backing dev info */
struct backing_dev_info bdi;
};
return get_fuse_inode(inode)->nodeid;
}
+/** Device operations */
+extern struct file_operations fuse_dev_operations;
+
/**
* This is the single global spinlock which protects FUSE's structures
*
* The following data is protected by this lock:
*
+ * - the private_data field of the device file
* - the s_fs_info field of the super block
+ * - unused_list, pending, processing lists in fuse_conn
+ * - the unique request ID counter reqctr in fuse_conn
* - the sb (super_block) field in fuse_conn
+ * - the file (device file) field in fuse_conn
*/
extern spinlock_t fuse_lock;
*/
void fuse_release_conn(struct fuse_conn *fc);
+/**
+ * Initialize the client device
+ */
+int fuse_dev_init(void);
+
+/**
+ * Cleanup the client device
+ */
+void fuse_dev_cleanup(void);
+
+/**
+ * Allocate a request
+ */
+struct fuse_req *fuse_request_alloc(void);
+
+/**
+ * Free a request
+ */
+void fuse_request_free(struct fuse_req *req);
+
+/**
+ * Reinitialize a request, the preallocated flag is left unmodified
+ */
+void fuse_reset_request(struct fuse_req *req);
+
+/**
+ * Reserve a preallocated request
+ */
+struct fuse_req *fuse_get_request(struct fuse_conn *fc);
+
+/**
+ * Reserve a preallocated request, only interruptible by SIGKILL
+ */
+struct fuse_req *fuse_get_request_nonint(struct fuse_conn *fc);
+
+/**
+ * Decrement reference count of a request. If count goes to zero put
+ * on unused list (preallocated) or free reqest (not preallocated).
+ */
+void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req);
+
+/**
+ * Send a request (synchronous, interruptible)
+ */
+void request_send(struct fuse_conn *fc, struct fuse_req *req);
+
+/**
+ * Send a request (synchronous, non-interruptible except by SIGKILL)
+ */
+void request_send_nonint(struct fuse_conn *fc, struct fuse_req *req);
+
+/**
+ * Send a request with no reply
+ */
+void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req);
+
+/**
+ * Send a request in the background
+ */
+void request_send_background(struct fuse_conn *fc, struct fuse_req *req);
+
+/**
+ * Send the INIT message
+ */
+void fuse_send_init(struct fuse_conn *fc);
projects / linux-2.6 / commitdiff