* Vivek Goyal ([email protected]) wrote:
> Doing posix locks with-in guest kernel are not sufficient if a file/dir
> is being shared by multiple guests. So we need the notion of daemon doing
> the locks which are visible to rest of the guests.
>
> Given posix locks are per process, one can not call posix lock API on host,
> otherwise bunch of basic posix locks properties are broken. For example,
> If two processes (A and B) in guest open the file and take locks on different
> sections of file, if one of the processes closes the fd, it will close
> fd on virtiofsd and all posix locks on file will go away. This means if
> process A closes the fd, then locks of process B will go away too.
>
> Similar other problems exist too.
>
> This patch set tries to emulate posix locks while using open file
> description locks provided on Linux.
>
> Daemon provides two options (-o posix_lock, -o no_posix_lock) to enable
> or disable posix locking in daemon. By default it is enabled.
>
> There are few issues though.
>
> - GETLK() returns pid of process holding lock. As we are emulating locks
> using OFD, and these locks are not per process and don't return pid
> of process, so GETLK() in guest does not reuturn process pid.
>
> - As of now only F_SETLK is supported and not F_SETLKW. We can't block
> the thread in virtiofsd for arbitrary long duration as there is only
> one thread serving the queue. That means unlock request will not make
> it to daemon and F_SETLKW will block infinitely and bring virtio-fs
> to a halt. This is a solvable problem though and will require significant
> changes in virtiofsd and kernel. Left as a TODO item for now.
>
> Signed-off-by: Vivek Goyal <[email protected]>
> ---
> contrib/virtiofsd/passthrough_ll.c | 185
> ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 184 insertions(+), 1 deletion(-)
>
> Index: qemu/contrib/virtiofsd/passthrough_ll.c
> ===================================================================
> --- qemu.orig/contrib/virtiofsd/passthrough_ll.c 2019-04-25
> 10:49:14.103386416 -0400
> +++ qemu/contrib/virtiofsd/passthrough_ll.c 2019-05-30 14:02:55.598483536
> -0400
> @@ -58,6 +58,12 @@
> #include <gmodule.h>
> #include "seccomp.h"
>
> +/* Keep track of inode posix locks for each owner. */
> +struct lo_inode_plock {
> + uint64_t lock_owner;
> + int fd; /* fd for OFD locks */
> +};
> +
> struct lo_map_elem {
> union {
> struct lo_inode *inode;
> @@ -86,6 +92,8 @@ struct lo_inode {
> struct lo_key key;
> uint64_t refcount; /* protected by lo->mutex */
> fuse_ino_t fuse_ino;
> + pthread_mutex_t mutex;
If this mutex is purely for posix_locks then there's probably a better
name.
> + GHashTable *posix_locks; /* protected by lo_inode->mutex */
> };
>
> struct lo_cred {
> @@ -105,6 +113,7 @@ struct lo_data {
> int norace;
> int writeback;
> int flock;
> + int posix_lock;
> int xattr;
> const char *source;
> double timeout;
> @@ -133,6 +142,10 @@ static const struct fuse_opt lo_opts[] =
> offsetof(struct lo_data, flock), 1 },
> { "no_flock",
> offsetof(struct lo_data, flock), 0 },
> + { "posix_lock",
> + offsetof(struct lo_data, posix_lock), 0 },
> + { "no_posix_lock",
> + offsetof(struct lo_data, posix_lock), 0 },
> { "xattr",
> offsetof(struct lo_data, xattr), 1 },
> { "no_xattr",
> @@ -362,13 +375,24 @@ static void lo_init(void *userdata,
> fprintf(stderr, "lo_init: activating flock locks\n");
> conn->want |= FUSE_CAP_FLOCK_LOCKS;
> }
> +
> + if (conn->capable & FUSE_CAP_POSIX_LOCKS) {
> + if (lo->posix_lock) {
> + if (lo->debug)
> + fprintf(stderr, "lo_init: activating posix
> locks\n");
> + conn->want |= FUSE_CAP_POSIX_LOCKS;
> + } else {
> + if (lo->debug)
> + fprintf(stderr, "lo_init: disabling posix
> locks\n");
> + conn->want &= ~FUSE_CAP_POSIX_LOCKS;
> + }
> + }
> if ((lo->cache == CACHE_NONE && !lo->readdirplus_set) ||
> lo->readdirplus_clear) {
> if (lo->debug)
> fprintf(stderr, "lo_init: disabling readdirplus\n");
> conn->want &= ~FUSE_CAP_READDIRPLUS;
> }
> -
> }
>
> static void lo_getattr(fuse_req_t req, fuse_ino_t ino,
> @@ -673,6 +697,8 @@ static int lo_do_lookup(fuse_req_t req,
> newfd = -1;
> inode->key.ino = e->attr.st_ino;
> inode->key.dev = e->attr.st_dev;
> + pthread_mutex_init(&inode->mutex, NULL);
> + inode->posix_locks = g_hash_table_new(g_direct_hash,
> g_direct_equal);
>
> pthread_mutex_lock(&lo->mutex);
> inode->fuse_ino = lo_add_inode_mapping(req, inode);
> @@ -1038,6 +1064,10 @@ static void unref_inode(struct lo_data *
> if (!inode->refcount) {
> lo_map_remove(&lo->ino_map, inode->fuse_ino);
> g_hash_table_remove(lo->inodes, &inode->key);
> + if (g_hash_table_size(inode->posix_locks)) {
> + warn("Hash table is not empty\n");
> + }
> + g_hash_table_destroy(inode->posix_locks);
> pthread_mutex_unlock(&lo->mutex);
> close(inode->fd);
pthread_mutex_destroy(&inode->mutex) ?
Other than that, and the naming, this looks OK to me, but I don't know
much about locks.
Dave
> free(inode);
> @@ -1379,6 +1409,131 @@ out:
> fuse_reply_create(req, &e, fi);
> }
>
> +/* Should be called with inode->mutex held */
> +static struct lo_inode_plock *lookup_create_plock_ctx(struct lo_data *lo,
> + struct lo_inode *inode, uint64_t lock_owner,
> + pid_t pid, int *err)
> +{
> + struct lo_inode_plock *plock;
> + char procname[64];
> + int fd;
> +
> + plock = g_hash_table_lookup(inode->posix_locks,
> + GUINT_TO_POINTER(lock_owner));
> +
> + if (plock)
> + return plock;
> +
> + plock = malloc(sizeof(struct lo_inode_plock));
> + if (!plock) {
> + *err = ENOMEM;
> + return NULL;
> + }
> +
> + /* Open another instance of file which can be used for ofd locks. */
> + sprintf(procname, "%i", inode->fd);
> +
> + /* TODO: What if file is not writable? */
> + fd = openat(lo->proc_self_fd, procname, O_RDWR);
> + if (fd == -1) {
> + *err = -errno;
> + free(plock);
> + return NULL;
> + }
> +
> + plock->lock_owner = lock_owner;
> + plock->fd = fd;
> + g_hash_table_insert(inode->posix_locks,
> + GUINT_TO_POINTER(plock->lock_owner), plock);
> + return plock;
> +}
> +
> +static void lo_getlk(fuse_req_t req, fuse_ino_t ino,
> + struct fuse_file_info *fi, struct flock *lock)
> +{
> + struct lo_data *lo = lo_data(req);
> + struct lo_inode *inode;
> + struct lo_inode_plock *plock;
> + int ret, saverr = 0;
> +
> + if (lo_debug(req))
> + fprintf(stderr, "lo_getlk(ino=%" PRIu64 ", flags=%d)"
> + " owner=0x%lx, l_type=%d l_start=0x%lx"
> + " l_len=0x%lx\n", ino, fi->flags, fi->lock_owner,
> + lock->l_type, lock->l_start, lock->l_len);
> +
> + inode = lo_inode(req, ino);
> + if (!inode) {
> + fuse_reply_err(req, EBADF);
> + return;
> + }
> +
> + pthread_mutex_lock(&inode->mutex);
> + plock = lookup_create_plock_ctx(lo, inode, fi->lock_owner, lock->l_pid,
> + &ret);
> + if (!plock) {
> + pthread_mutex_unlock(&inode->mutex);
> + fuse_reply_err(req, ret);
> + return;
> + }
> +
> + ret = fcntl(plock->fd, F_OFD_GETLK, lock);
> + if (ret == -1)
> + saverr = errno;
> + pthread_mutex_unlock(&inode->mutex);
> +
> + if (saverr)
> + fuse_reply_err(req, saverr);
> + else
> + fuse_reply_lock(req, lock);
> +}
> +
> +static void lo_setlk(fuse_req_t req, fuse_ino_t ino,
> + struct fuse_file_info *fi, struct flock *lock, int sleep)
> +{
> + struct lo_data *lo = lo_data(req);
> + struct lo_inode *inode;
> + struct lo_inode_plock *plock;
> + int ret, saverr = 0;
> +
> + if (lo_debug(req))
> + fprintf(stderr, "lo_setlk(ino=%" PRIu64 ", flags=%d)"
> + " cmd=%d pid=%d owner=0x%lx sleep=%d l_whence=%d"
> + " l_start=0x%lx l_len=0x%lx\n", ino, fi->flags,
> + lock->l_type, lock->l_pid, fi->lock_owner, sleep,
> + lock->l_whence, lock->l_start, lock->l_len);
> +
> + if (sleep) {
> + fuse_reply_err(req, EOPNOTSUPP);
> + return;
> + }
> +
> + inode = lo_inode(req, ino);
> + if (!inode) {
> + fuse_reply_err(req, EBADF);
> + return;
> + }
> +
> + pthread_mutex_lock(&inode->mutex);
> + plock = lookup_create_plock_ctx(lo, inode, fi->lock_owner, lock->l_pid,
> + &ret);
> +
> + if (!plock) {
> + pthread_mutex_unlock(&inode->mutex);
> + fuse_reply_err(req, ret);
> + return;
> + }
> +
> + /* TODO: Is it alright to modify flock? */
> + lock->l_pid = 0;
> + ret = fcntl(plock->fd, F_OFD_SETLK, lock);
> + if (ret == -1) {
> + saverr = errno;
> + }
> + pthread_mutex_unlock(&inode->mutex);
> + fuse_reply_err(req, saverr);
> +}
> +
> static void lo_fsyncdir(fuse_req_t req, fuse_ino_t ino, int datasync,
> struct fuse_file_info *fi)
> {
> @@ -1476,6 +1631,31 @@ static void lo_flush(fuse_req_t req, fus
> {
> int res;
> (void) ino;
> + struct lo_inode *inode;
> + struct lo_inode_plock *plock;
> +
> + inode = lo_inode(req, ino);
> + if (!inode) {
> + fuse_reply_err(req, EBADF);
> + return;
> + }
> +
> + /* An fd is going away. Cleanup associated posix locks */
> + pthread_mutex_lock(&inode->mutex);
> + plock = g_hash_table_lookup(inode->posix_locks,
> + GUINT_TO_POINTER(fi->lock_owner));
> + if (plock) {
> + g_hash_table_remove(inode->posix_locks,
> + GUINT_TO_POINTER(fi->lock_owner));
> + /*
> + * We had used open() for locks and had only one fd. So
> + * closing this fd should release all OFD locks.
> + */
> + close(plock->fd);
> + free(plock);
> + }
> + pthread_mutex_unlock(&inode->mutex);
> +
> res = close(dup(lo_fi_fd(req, fi)));
> fuse_reply_err(req, res == -1 ? errno : 0);
> }
> @@ -1963,6 +2143,8 @@ static struct fuse_lowlevel_ops lo_oper
> .releasedir = lo_releasedir,
> .fsyncdir = lo_fsyncdir,
> .create = lo_create,
> + .getlk = lo_getlk,
> + .setlk = lo_setlk,
> .open = lo_open,
> .release = lo_release,
> .flush = lo_flush,
> @@ -2189,6 +2371,7 @@ int main(int argc, char *argv[])
> struct fuse_cmdline_opts opts;
> struct lo_data lo = { .debug = 0,
> .writeback = 0,
> + .posix_lock = 1,
> .proc_self_fd = -1,
> };
> struct lo_map_elem *root_elem;
--
Dr. David Alan Gilbert / [email protected] / Manchester, UK
