Merge remote-tracking branch 'remotes/gkurz/tags/9p-next-2020-05-26' into staging

- fix build with musl libc
- fix potential deadlock of QEMU main event loop (cannot be hit with linux
  client)
- revert 9pfs reply truncation (LP 1877688)
- xen backend waits for client to free space on the reply ring instead of
  truncating or disconnecting

# gpg: Signature made Tue 26 May 2020 10:36:23 BST
# gpg:                using RSA key B4828BAF943140CEF2A3491071D4D5E5822F73D6
# gpg: Good signature from "Greg Kurz <groug@kaod.org>" [full]
# gpg:                 aka "Gregory Kurz <gregory.kurz@free.fr>" [full]
# gpg:                 aka "[jpeg image of size 3330]" [full]
# Primary key fingerprint: B482 8BAF 9431 40CE F2A3  4910 71D4 D5E5 822F 73D6

* remotes/gkurz/tags/9p-next-2020-05-26:
  xen/9pfs: increase max ring order to 9
  xen/9pfs: yield when there isn't enough room on the ring
  Revert "9p: init_in_iov_from_pdu can truncate the size"
  9p: Lock directory streams with a CoMutex
  9pfs: include linux/limits.h for XATTR_SIZE_MAX

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

1 files changed, 28 insertions, 12 deletions

diff --git a/hw/9pfs/xen-9p-backend.c b/hw/9pfs/xen-9p-backend.c
index f04caabfe5..a969fcc54c 100644
--- a/hw/9pfs/xen-9p-backend.c
+++ b/hw/9pfs/xen-9p-backend.c
@@ -21,7 +21,7 @@
 
 #define VERSIONS "1"
 #define MAX_RINGS 8
-#define MAX_RING_ORDER 8
+#define MAX_RING_ORDER 9
 
 typedef struct Xen9pfsRing {
     struct Xen9pfsDev *priv;
@@ -37,6 +37,7 @@ typedef struct Xen9pfsRing {
 
     struct iovec *sg;
     QEMUBH *bh;
+    Coroutine *co;
 
     /* local copies, so that we can read/write PDU data directly from
      * the ring */
@@ -188,7 +189,7 @@ static void xen_9pfs_init_out_iov_from_pdu(V9fsPDU *pdu,
 static void xen_9pfs_init_in_iov_from_pdu(V9fsPDU *pdu,
                                           struct iovec **piov,
                                           unsigned int *pniov,
-                                          size_t *size)
+                                          size_t size)
 {
     Xen9pfsDev *xen_9pfs = container_of(pdu->s, Xen9pfsDev, state);
     Xen9pfsRing *ring = &xen_9pfs->rings[pdu->tag % xen_9pfs->num_rings];
@@ -198,19 +199,20 @@ static void xen_9pfs_init_in_iov_from_pdu(V9fsPDU *pdu,
     g_free(ring->sg);
 
     ring->sg = g_new0(struct iovec, 2);
-    xen_9pfs_in_sg(ring, ring->sg, &num, pdu->idx, *size);
+    ring->co = qemu_coroutine_self();
+    /* make sure other threads see ring->co changes before continuing */
+    smp_wmb();
 
+again:
+    xen_9pfs_in_sg(ring, ring->sg, &num, pdu->idx, size);
     buf_size = iov_size(ring->sg, num);
-    if (buf_size  < P9_IOHDRSZ) {
-        xen_pv_printf(&xen_9pfs->xendev, 0, "Xen 9pfs reply type %d needs "
-                      "%zu bytes, buffer has %zu, less than minimum\n",
-                      pdu->id + 1, *size, buf_size);
-        xen_be_set_state(&xen_9pfs->xendev, XenbusStateClosing);
-        xen_9pfs_disconnect(&xen_9pfs->xendev);
-    }
-    if (buf_size  < *size) {
-        *size = buf_size;
+    if (buf_size  < size) {
+        qemu_coroutine_yield();
+        goto again;
     }
+    ring->co = NULL;
+    /* make sure other threads see ring->co changes before continuing */
+    smp_wmb();
 
     *piov = ring->sg;
     *pniov = num;
@@ -295,6 +297,20 @@ static int xen_9pfs_receive(Xen9pfsRing *ring)
 static void xen_9pfs_bh(void *opaque)
 {
     Xen9pfsRing *ring = opaque;
+    bool wait;
+
+again:
+    wait = ring->co != NULL && qemu_coroutine_entered(ring->co);
+    /* paired with the smb_wmb barriers in xen_9pfs_init_in_iov_from_pdu */
+    smp_rmb();
+    if (wait) {
+        cpu_relax();
+        goto again;
+    }
+
+    if (ring->co != NULL) {
+        qemu_coroutine_enter_if_inactive(ring->co);
+    }
     xen_9pfs_receive(ring);
 }