[Qemu-devel] [PATCH 1/2] qemu-virto9p: Implement TLOCK

["M. Mohan Kumar" <mohan@in.ibm.com>]

Synopsis

    size[4] TLock tag[2] fid[4] flock[n]
    size[4] RLock tag[2] status[1]

Description

Tlock is used to acquire/release byte range posix locks on a file
identified by given fid. The reply contains status of the lock request

    flock structure:
        type[1] - Type of lock: F_RDLCK, F_WRLCK, F_UNLCK
        flags[4] - Flags could be either of
          P9_LOCK_FLAGS_BLOCK(1) - Blocked lock request, if there is a
            conflicting lock exists, wait for that lock to be released.
          P9_LOCK_FLAGS_RECLAIM(2) - Reclaim lock request, used when client is
            trying to reclaim a lock after a server restrart (due to crash)
        start[8] - Starting offset for lock
        length[8] - Number of bytes to lock
          If length is 0, lock all bytes starting at the location 'start'
          through to the end of file
        pid[4] - PID of the process that wants to take lock
        client_id[4] - Unique client id

        status[1] - Status of the lock request, can be
          P9_LOCK_SUCCESS(0), P9_LOCK_BLOCKED(1), P9_LOCK_ERROR(2) or
          P9_LOCK_GRACE(3)
          P9_LOCK_SUCCESS - Request was successful
          P9_LOCK_BLOCKED - A conflicting lock is held by another process
          P9_LOCK_ERROR - Error while processing the lock request
          P9_LOCK_GRACE - Server is in grace period, it can't accept new lock
                requests in this period (except locks with
                P9_LOCK_FLAGS_RECLAIM flag set)

Signed-off-by: M. Mohan Kumar <mohan@in.ibm.com>
---
 hw/virtio-9p-debug.c |   14 ++++++++++++++
 hw/virtio-9p.c       |   50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 hw/virtio-9p.h       |   30 ++++++++++++++++++++++++++++++
 3 files changed, 94 insertions(+), 0 deletions(-)

diff --git a/hw/virtio-9p-debug.c b/hw/virtio-9p-debug.c
index 6f6a0ec..045774f 100644
--- a/hw/virtio-9p-debug.c
+++ b/hw/virtio-9p-debug.c
@@ -588,6 +588,20 @@ void pprint_pdu(V9fsPDU *pdu)
     case P9_RXATTRCREATE:
         fprintf(llogfile, "RXATTRCREATE: (");
         break;
+    case P9_TLOCK:
+        fprintf(llogfile, "TLOCK: (");
+        pprint_int32(pdu, 0, &offset, "fid");
+        pprint_int8(pdu, 0, &offset, ", type");
+        pprint_int32(pdu, 0, &offset, ", flags");
+        pprint_int64(pdu, 0, &offset, ", start");
+        pprint_int64(pdu, 0, &offset, ", length");
+        pprint_int32(pdu, 0, &offset, ", proc_id");
+        pprint_str(pdu, 0, &offset, ", client_id");
+        break;
+    case P9_RLOCK:
+        fprintf(llogfile, "RLOCK: (");
+        pprint_int8(pdu, 0, &offset, "status");
+        break;
     default:
         fprintf(llogfile, "unknown(%d): (", pdu->id);
         break;
diff --git a/hw/virtio-9p.c b/hw/virtio-9p.c
index 32fa3bc..b3d55f1 100644
--- a/hw/virtio-9p.c
+++ b/hw/virtio-9p.c
@@ -3150,6 +3150,55 @@ out:
     qemu_free(vs);
 }
 
+/*
+ * Implement posix byte range locking code
+ * Server side handling of locking code is very simple, because 9p server in QEMU
+ * can handle only one client.  And most of the lock handling (like conflict,
+ * merging) etc is done by the VFS layer itself, so no need to do any thing in
+ * qemu 9p server side lock code path.
+ * So when a TLOCK request comes, always return success
+ */
+
+static void v9fs_lock(V9fsState *s, V9fsPDU *pdu)
+{
+    int32_t fid, err = 0;
+    V9fsLockState *vs;
+
+    vs = qemu_mallocz(sizeof(*vs));
+    vs->pdu = pdu;
+    vs->offset = 7;
+
+    vs->flock = qemu_malloc(sizeof(*vs->flock));
+    pdu_unmarshal(vs->pdu, vs->offset, "dbdqqds", &fid, &vs->flock->type,
+                &vs->flock->flags, &vs->flock->start, &vs->flock->length,
+                            &vs->flock->proc_id, &vs->flock->client_id);
+
+    vs->status = P9_LOCK_ERROR;
+
+    /* We support only block flag now (that too ignored currently) */
+    if (vs->flock->flags & ~P9_LOCK_FLAGS_BLOCK) {
+        err = -EINVAL;
+        goto out;
+    }
+    vs->fidp = lookup_fid(s, fid);
+    if (vs->fidp == NULL) {
+        err = -ENOENT;
+        goto out;
+    }
+
+    err = v9fs_do_fstat(s, vs->fidp->fs.fd, &vs->stbuf);
+    if (err < 0) {
+        err = -errno;
+        goto out;
+    }
+    vs->status = P9_LOCK_SUCCESS;
+out:
+    vs->offset += pdu_marshal(vs->pdu, vs->offset, "b", vs->status);
+    complete_pdu(s, vs->pdu, err);
+    qemu_free(vs->flock);
+    qemu_free(vs);
+}
+
 static void v9fs_mkdir_post_lstat(V9fsState *s, V9fsMkState *vs, int err)
 {
     if (err == -1) {
@@ -3412,6 +3461,7 @@ static pdu_handler_t *pdu_handlers[] = {
     [P9_TXATTRCREATE] = v9fs_xattrcreate,
     [P9_TMKNOD] = v9fs_mknod,
     [P9_TRENAME] = v9fs_rename,
+    [P9_TLOCK] = v9fs_lock,
     [P9_TMKDIR] = v9fs_mkdir,
     [P9_TVERSION] = v9fs_version,
     [P9_TLOPEN] = v9fs_open,
diff --git a/hw/virtio-9p.h b/hw/virtio-9p.h
index 0816ad6..4555f39 100644
--- a/hw/virtio-9p.h
+++ b/hw/virtio-9p.h
@@ -37,6 +37,8 @@ enum {
     P9_RXATTRCREATE,
     P9_TREADDIR = 40,
     P9_RREADDIR,
+    P9_TLOCK = 52,
+    P9_RLOCK,
     P9_TLINK = 70,
     P9_RLINK,
     P9_TMKDIR = 72,
@@ -434,6 +436,34 @@ typedef struct V9fsXattrState
     void *value;
 } V9fsXattrState;
 
+#define P9_LOCK_SUCCESS 0
+#define P9_LOCK_BLOCKED 1
+#define P9_LOCK_ERROR 2
+#define P9_LOCK_GRACE 3
+
+#define P9_LOCK_FLAGS_BLOCK 1
+#define P9_LOCK_FLAGS_RECLAIM 2
+
+typedef struct V9fsFlock
+{
+    uint8_t type;
+    uint32_t flags;
+    uint64_t start; /* absolute offset */
+    uint64_t length;
+    uint32_t proc_id;
+    V9fsString client_id;
+} V9fsFlock;
+
+typedef struct V9fsLockState
+{
+    V9fsPDU *pdu;
+    size_t offset;
+    int8_t status;
+    struct stat stbuf;
+    V9fsFidState *fidp;
+    V9fsFlock *flock;
+} V9fsLockState;
+
 extern size_t pdu_packunpack(void *addr, struct iovec *sg, int sg_count,
                             size_t offset, size_t size, int pack);
 
-- 
1.7.0.4