[virtio-9p] Define and implement TSYMLINK for 9P2000.L

This patch implements creating a symlink for TSYMLINK request
and responds with RSYMLINK. In the case of error, we return RERROR.

SYNOPSIS

    size[4] Tsymlink tag[2] fid[4] name[s] symtgt[s] gid[4]

    size[4] Rsymlink tag[2] qid[13]

    DESCRIPTION

    Create a symbolic link named 'name' pointing to 'symtgt'.
    gid represents the effective group id of the caller.
    The  permissions of a symbolic link are irrelevant hence it is omitted
    from the protocol.

Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>

hw/virtio-9p-debug.c

@@ -464,6 +464,17 @@ void pprint_pdu(V9fsPDU *pdu)
         pprint_qid(pdu, 1, &offset, "qid");
         pprint_int32(pdu, 1, &offset, ", iounit");
         break;
+    case P9_TSYMLINK:
+        fprintf(llogfile, "TSYMLINK: (");
+        pprint_int32(pdu, 0, &offset, "fid");
+        pprint_str(pdu, 0, &offset, ", name");
+        pprint_str(pdu, 0, &offset, ", symname");
+        pprint_int32(pdu, 0, &offset, ", gid");
+        break;
+    case P9_RSYMLINK:
+        fprintf(llogfile, "RSYMLINK: (");
+        pprint_qid(pdu, 1, &offset, "qid");
+        break;
     case P9_TREAD:
         fprintf(llogfile, "TREAD: (");
         pprint_int32(pdu, 0, &offset, "fid");

hw/virtio-9p.c

@@ -200,15 +200,16 @@ static int v9fs_do_open2(V9fsState *s, V9fsCreateState *vs)
     return s->ops->open2(&s->ctx, vs->fullname.data, flags, &cred);
 }
 
-static int v9fs_do_symlink(V9fsState *s, V9fsCreateState *vs)
+static int v9fs_do_symlink(V9fsState *s, V9fsFidState *fidp,
+        const char *oldpath, const char *newpath, gid_t gid)
 {
     FsCred cred;
     cred_init(&cred);
-    cred.fc_uid = vs->fidp->uid;
-    cred.fc_mode = vs->perm | 0777;
+    cred.fc_uid = fidp->uid;
+    cred.fc_gid = gid;
+    cred.fc_mode = 0777;
 
-    return s->ops->symlink(&s->ctx, vs->extension.data, vs->fullname.data,
-            &cred);
+    return s->ops->symlink(&s->ctx, oldpath, newpath, &cred);
 }
 
 static int v9fs_do_link(V9fsState *s, V9fsString *oldpath, V9fsString *newpath)
@@ -2212,7 +2213,8 @@ static void v9fs_create_post_lstat(V9fsState *s, V9fsCreateState *vs, int err)
         err = v9fs_do_mkdir(s, vs);
         v9fs_create_post_mkdir(s, vs, err);
     } else if (vs->perm & P9_STAT_MODE_SYMLINK) {
-        err = v9fs_do_symlink(s, vs);
+        err = v9fs_do_symlink(s, vs->fidp, vs->extension.data,
+                vs->fullname.data, -1);
         v9fs_create_post_perms(s, vs, err);
     } else if (vs->perm & P9_STAT_MODE_LINK) {
         int32_t nfid = atoi(vs->extension.data);
@@ -2301,6 +2303,69 @@ out:
     qemu_free(vs);
 }
 
+static void v9fs_post_symlink(V9fsState *s, V9fsSymlinkState *vs, int err)
+{
+    if (err == 0) {
+        stat_to_qid(&vs->stbuf, &vs->qid);
+        vs->offset += pdu_marshal(vs->pdu, vs->offset, "Q", &vs->qid);
+        err = vs->offset;
+    } else {
+        err = -errno;
+    }
+    complete_pdu(s, vs->pdu, err);
+    v9fs_string_free(&vs->name);
+    v9fs_string_free(&vs->symname);
+    v9fs_string_free(&vs->fullname);
+    qemu_free(vs);
+}
+
+static void v9fs_symlink_post_do_symlink(V9fsState *s, V9fsSymlinkState *vs,
+        int err)
+{
+    if (err) {
+        goto out;
+    }
+    err = v9fs_do_lstat(s, &vs->fullname, &vs->stbuf);
+out:
+    v9fs_post_symlink(s, vs, err);
+}
+
+static void v9fs_symlink(V9fsState *s, V9fsPDU *pdu)
+{
+    int32_t dfid;
+    V9fsSymlinkState *vs;
+    int err = 0;
+    gid_t gid;
+
+    vs = qemu_malloc(sizeof(*vs));
+    vs->pdu = pdu;
+    vs->offset = 7;
+
+    v9fs_string_init(&vs->fullname);
+
+    pdu_unmarshal(vs->pdu, vs->offset, "dssd", &dfid, &vs->name,
+            &vs->symname, &gid);
+
+    vs->dfidp = lookup_fid(s, dfid);
+    if (vs->dfidp == NULL) {
+        err = -EINVAL;
+        goto out;
+    }
+
+    v9fs_string_sprintf(&vs->fullname, "%s/%s", vs->dfidp->path.data,
+            vs->name.data);
+    err = v9fs_do_symlink(s, vs->dfidp, vs->symname.data,
+            vs->fullname.data, gid);
+    v9fs_symlink_post_do_symlink(s, vs, err);
+    return;
+
+out:
+    complete_pdu(s, vs->pdu, err);
+    v9fs_string_free(&vs->name);
+    v9fs_string_free(&vs->symname);
+    qemu_free(vs);
+}
+
 static void v9fs_flush(V9fsState *s, V9fsPDU *pdu)
 {
     /* A nop call with no return */
@@ -2718,6 +2783,7 @@ static pdu_handler_t *pdu_handlers[] = {
 #endif
     [P9_TFLUSH] = v9fs_flush,
     [P9_TLINK] = v9fs_link,
+    [P9_TSYMLINK] = v9fs_symlink,
     [P9_TCREATE] = v9fs_create,
     [P9_TWRITE] = v9fs_write,
     [P9_TWSTAT] = v9fs_wstat,

hw/virtio-9p.h

@@ -15,6 +15,8 @@
 enum {
     P9_TSTATFS = 8,
     P9_RSTATFS,
+    P9_TSYMLINK = 16,
+    P9_RSYMLINK,
     P9_TGETATTR = 24,
     P9_RGETATTR,
     P9_TSETATTR = 26,
@@ -294,6 +296,18 @@ typedef struct V9fsWstatState
     V9fsString nname;
 } V9fsWstatState;
 
+typedef struct V9fsSymlinkState
+{
+    V9fsPDU *pdu;
+    size_t offset;
+    V9fsString name;
+    V9fsString symname;
+    V9fsString fullname;
+    V9fsFidState *dfidp;
+    V9fsQID qid;
+    struct stat stbuf;
+} V9fsSymlinkState;
+
 typedef struct V9fsIattr
 {
     int32_t valid;