Merge remote-tracking branch 'remotes/cschoenebeck/tags/pull-9p-20210705' into staging

9pfs: misc patches

* Add link to 9p developer docs.

* Fix runtime check whether client supplied relative path is the export
  root.

* Performance optimization of Twalk requests.

* Code cleanup.

# gpg: Signature made Mon 05 Jul 2021 12:13:34 BST
# gpg:                using RSA key 96D8D110CF7AF8084F88590134C2B58765A47395
# gpg:                issuer "qemu_oss@crudebyte.com"
# gpg: Good signature from "Christian Schoenebeck <qemu_oss@crudebyte.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: ECAB 1A45 4014 1413 BA38  4926 30DB 47C3 A012 D5F4
#      Subkey fingerprint: 96D8 D110 CF7A F808 4F88  5901 34C2 B587 65A4 7395

* remotes/cschoenebeck/tags/pull-9p-20210705:
  9pfs: reduce latency of Twalk
  9pfs: drop root_qid
  9pfs: replace not_same_qid() by same_stat_id()
  9pfs: drop fid_to_qid()
  9pfs: capture root stat
  9pfs: fix not_same_qid()
  9pfs: simplify v9fs_walk()
  9pfs: add link to 9p developer docs

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

16 files changed, 166 insertions, 48 deletions

diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index af52c1d..210d9e7 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -10,6 +10,11 @@
  * the COPYING file in the top-level directory.
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "9p.h"
 #include "9p-local.h"
diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c
index bbf8906..eadae27 100644
--- a/hw/9pfs/9p-posix-acl.c
+++ b/hw/9pfs/9p-posix-acl.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "qemu/xattr.h"
 #include "9p.h"
diff --git a/hw/9pfs/9p-proxy.c b/hw/9pfs/9p-proxy.c
index 4aa4e0a..09bd9f1 100644
--- a/hw/9pfs/9p-proxy.c
+++ b/hw/9pfs/9p-proxy.c
@@ -10,6 +10,11 @@
  * the COPYING file in the top-level directory.
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include <sys/socket.h>
 #include <sys/un.h>
diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c
index 473ef91..b38088e 100644
--- a/hw/9pfs/9p-synth.c
+++ b/hw/9pfs/9p-synth.c
@@ -12,6 +12,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "9p.h"
 #include "fsdev/qemu-fsdev.h"
diff --git a/hw/9pfs/9p-util.c b/hw/9pfs/9p-util.c
index 614b7fc..3221d9b 100644
--- a/hw/9pfs/9p-util.c
+++ b/hw/9pfs/9p-util.c
@@ -10,6 +10,11 @@
  * See the COPYING file in the top-level directory.
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "qemu/xattr.h"
 #include "9p-util.h"
diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c
index 2c90817..f2ae958 100644
--- a/hw/9pfs/9p-xattr-user.c
+++ b/hw/9pfs/9p-xattr-user.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "9p.h"
 #include "fsdev/file-op-9p.h"
diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c
index c696d8f..9ae69dd 100644
--- a/hw/9pfs/9p-xattr.c
+++ b/hw/9pfs/9p-xattr.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "9p.h"
 #include "fsdev/file-op-9p.h"
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 134806d..2815257 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include <glib/gprintf.h>
 #include "hw/virtio/virtio.h"
@@ -966,23 +971,6 @@ static int stat_to_qid(V9fsPDU *pdu, const struct stat *stbuf, V9fsQID *qidp)
     return 0;
 }
 
-static int coroutine_fn fid_to_qid(V9fsPDU *pdu, V9fsFidState *fidp,
-                                   V9fsQID *qidp)
-{
-    struct stat stbuf;
-    int err;
-
-    err = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
-    if (err < 0) {
-        return err;
-    }
-    err = stat_to_qid(pdu, &stbuf, qidp);
-    if (err < 0) {
-        return err;
-    }
-    return 0;
-}
-
 V9fsPDU *pdu_alloc(V9fsState *s)
 {
     V9fsPDU *pdu = NULL;
@@ -1395,6 +1383,7 @@ static void coroutine_fn v9fs_attach(void *opaque)
     size_t offset = 7;
     V9fsQID qid;
     ssize_t err;
+    struct stat stbuf;
 
     v9fs_string_init(&uname);
     v9fs_string_init(&aname);
@@ -1417,7 +1406,13 @@ static void coroutine_fn v9fs_attach(void *opaque)
         clunk_fid(s, fid);
         goto out;
     }
-    err = fid_to_qid(pdu, fidp, &qid);
+    err = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
+    if (err < 0) {
+        err = -EINVAL;
+        clunk_fid(s, fid);
+        goto out;
+    }
+    err = stat_to_qid(pdu, &stbuf, &qid);
     if (err < 0) {
         err = -EINVAL;
         clunk_fid(s, fid);
@@ -1449,7 +1444,7 @@ static void coroutine_fn v9fs_attach(void *opaque)
     }
     err += offset;
 
-    memcpy(&s->root_qid, &qid, sizeof(qid));
+    memcpy(&s->root_st, &stbuf, sizeof(stbuf));
     trace_v9fs_attach_return(pdu->tag, pdu->id,
                              qid.type, qid.version, qid.path);
 out:
@@ -1700,12 +1695,9 @@ static bool name_is_illegal(const char *name)
     return !*name || strchr(name, '/') != NULL;
 }
 
-static bool not_same_qid(const V9fsQID *qid1, const V9fsQID *qid2)
+static bool same_stat_id(const struct stat *a, const struct stat *b)
 {
-    return
-        qid1->type != qid2->type ||
-        qid1->version != qid2->version ||
-        qid1->path != qid2->path;
+    return a->st_dev == b->st_dev && a->st_ino == b->st_ino;
 }
 
 static void coroutine_fn v9fs_walk(void *opaque)
@@ -1713,9 +1705,9 @@ static void coroutine_fn v9fs_walk(void *opaque)
     int name_idx;
     V9fsQID *qids = NULL;
     int i, err = 0;
-    V9fsPath dpath, path;
+    V9fsPath dpath, path, *pathes = NULL;
     uint16_t nwnames;
-    struct stat stbuf;
+    struct stat stbuf, fidst, *stbufs = NULL;
     size_t offset = 7;
     int32_t fid, newfid;
     V9fsString *wnames = NULL;
@@ -1734,9 +1726,15 @@ static void coroutine_fn v9fs_walk(void *opaque)
 
     trace_v9fs_walk(pdu->tag, pdu->id, fid, newfid, nwnames);
 
-    if (nwnames && nwnames <= P9_MAXWELEM) {
+    if (nwnames > P9_MAXWELEM) {
+        err = -EINVAL;
+        goto out_nofid;
+    }
+    if (nwnames) {
         wnames = g_new0(V9fsString, nwnames);
         qids   = g_new0(V9fsQID, nwnames);
+        stbufs = g_new0(struct stat, nwnames);
+        pathes = g_new0(V9fsPath, nwnames);
         for (i = 0; i < nwnames; i++) {
             err = pdu_unmarshal(pdu, offset, "s", &wnames[i]);
             if (err < 0) {
@@ -1748,9 +1746,6 @@ static void coroutine_fn v9fs_walk(void *opaque)
             }
             offset += err;
         }
-    } else if (nwnames > P9_MAXWELEM) {
-        err = -EINVAL;
-        goto out_nofid;
     }
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
@@ -1760,35 +1755,85 @@ static void coroutine_fn v9fs_walk(void *opaque)
 
     v9fs_path_init(&dpath);
     v9fs_path_init(&path);
+    /*
+     * Both dpath and path initially point to fidp.
+     * Needed to handle request with nwnames == 0
+     */
+    v9fs_path_copy(&dpath, &fidp->path);
+    v9fs_path_copy(&path, &fidp->path);
 
-    err = fid_to_qid(pdu, fidp, &qid);
+    /*
+     * To keep latency (i.e. overall execution time for processing this
+     * Twalk client request) as small as possible, run all the required fs
+     * driver code altogether inside the following block.
+     */
+    v9fs_co_run_in_worker({
+        if (v9fs_request_cancelled(pdu)) {
+            err = -EINTR;
+            break;
+        }
+        err = s->ops->lstat(&s->ctx, &dpath, &fidst);
+        if (err < 0) {
+            err = -errno;
+            break;
+        }
+        stbuf = fidst;
+        for (name_idx = 0; name_idx < nwnames; name_idx++) {
+            if (v9fs_request_cancelled(pdu)) {
+                err = -EINTR;
+                break;
+            }
+            if (!same_stat_id(&pdu->s->root_st, &stbuf) ||
+                strcmp("..", wnames[name_idx].data))
+            {
+                err = s->ops->name_to_path(&s->ctx, &dpath,
+                                        wnames[name_idx].data, &path);
+                if (err < 0) {
+                    err = -errno;
+                    break;
+                }
+                if (v9fs_request_cancelled(pdu)) {
+                    err = -EINTR;
+                    break;
+                }
+                err = s->ops->lstat(&s->ctx, &path, &stbuf);
+                if (err < 0) {
+                    err = -errno;
+                    break;
+                }
+                stbufs[name_idx] = stbuf;
+                v9fs_path_copy(&dpath, &path);
+                v9fs_path_copy(&pathes[name_idx], &path);
+            }
+        }
+    });
+    /*
+     * Handle all the rest of this Twalk request on main thread ...
+     */
     if (err < 0) {
         goto out;
     }
 
-    /*
-     * Both dpath and path initially poin to fidp.
-     * Needed to handle request with nwnames == 0
-     */
+    err = stat_to_qid(pdu, &fidst, &qid);
+    if (err < 0) {
+        goto out;
+    }
+    stbuf = fidst;
+
+    /* reset dpath and path */
     v9fs_path_copy(&dpath, &fidp->path);
     v9fs_path_copy(&path, &fidp->path);
-    for (name_idx = 0; name_idx < nwnames; name_idx++) {
-        if (not_same_qid(&pdu->s->root_qid, &qid) ||
-            strcmp("..", wnames[name_idx].data)) {
-            err = v9fs_co_name_to_path(pdu, &dpath, wnames[name_idx].data,
-                                       &path);
-            if (err < 0) {
-                goto out;
-            }
 
-            err = v9fs_co_lstat(pdu, &path, &stbuf);
-            if (err < 0) {
-                goto out;
-            }
+    for (name_idx = 0; name_idx < nwnames; name_idx++) {
+        if (!same_stat_id(&pdu->s->root_st, &stbuf) ||
+            strcmp("..", wnames[name_idx].data))
+        {
+            stbuf = stbufs[name_idx];
             err = stat_to_qid(pdu, &stbuf, &qid);
             if (err < 0) {
                 goto out;
             }
+            v9fs_path_copy(&path, &pathes[name_idx]);
             v9fs_path_copy(&dpath, &path);
         }
         memcpy(&qids[name_idx], &qid, sizeof(qid));
@@ -1824,9 +1869,12 @@ out_nofid:
     if (nwnames && nwnames <= P9_MAXWELEM) {
         for (name_idx = 0; name_idx < nwnames; name_idx++) {
             v9fs_string_free(&wnames[name_idx]);
+            v9fs_path_free(&pathes[name_idx]);
         }
         g_free(wnames);
         g_free(qids);
+        g_free(stbufs);
+        g_free(pathes);
     }
 }
 
diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
index 0038159..1567b67 100644
--- a/hw/9pfs/9p.h
+++ b/hw/9pfs/9p.h
@@ -355,7 +355,7 @@ struct V9fsState {
     int32_t root_fid;
     Error *migration_blocker;
     V9fsConf fsconf;
-    V9fsQID root_qid;
+    struct stat root_st;
     dev_t dev_id;
     struct qht qpd_table;
     struct qht qpp_table;
diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c
index 1f70a58..032cce0 100644
--- a/hw/9pfs/codir.c
+++ b/hw/9pfs/codir.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "fsdev/qemu-fsdev.h"
 #include "qemu/thread.h"
diff --git a/hw/9pfs/cofile.c b/hw/9pfs/cofile.c
index 83bb6c1..20f93a9 100644
--- a/hw/9pfs/cofile.c
+++ b/hw/9pfs/cofile.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "fsdev/qemu-fsdev.h"
 #include "qemu/thread.h"
diff --git a/hw/9pfs/cofs.c b/hw/9pfs/cofs.c
index 0b321b4..9d0adc2 100644
--- a/hw/9pfs/cofs.c
+++ b/hw/9pfs/cofs.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "fsdev/qemu-fsdev.h"
 #include "qemu/thread.h"
diff --git a/hw/9pfs/coth.c b/hw/9pfs/coth.c
index 9778f24..2802d41 100644
--- a/hw/9pfs/coth.c
+++ b/hw/9pfs/coth.c
@@ -12,6 +12,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "block/thread-pool.h"
 #include "qemu/coroutine.h"
diff --git a/hw/9pfs/coxattr.c b/hw/9pfs/coxattr.c
index 0e00ffa..dbcd09e 100644
--- a/hw/9pfs/coxattr.c
+++ b/hw/9pfs/coxattr.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "fsdev/qemu-fsdev.h"
 #include "qemu/thread.h"
diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
index 14371a7..54ee93b 100644
--- a/hw/9pfs/virtio-9p-device.c
+++ b/hw/9pfs/virtio-9p-device.c
@@ -11,6 +11,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 #include "hw/virtio/virtio.h"
 #include "qemu/sockets.h"
diff --git a/hw/9pfs/xen-9p-backend.c b/hw/9pfs/xen-9p-backend.c
index a969fcc..65c4979 100644
--- a/hw/9pfs/xen-9p-backend.c
+++ b/hw/9pfs/xen-9p-backend.c
@@ -8,6 +8,11 @@
  *
  */
 
+/*
+ * Not so fast! You might want to read the 9p developer docs first:
+ * https://wiki.qemu.org/Documentation/9p
+ */
+
 #include "qemu/osdep.h"
 
 #include "hw/9pfs/9p.h"