[PATCH v6 51/51] hw/xen: Add basic ring handling to xenstore

[David Woodhouse <dwmw2@infradead.org>]

From: David Woodhouse <dwmw@amazon.co.uk>

Extract requests, return ENOSYS to all of them. This is enough to allow
older Linux guests to boot, as they need *something* back but it doesn't
matter much what.

In the first instance we're likely to wire this up over a UNIX socket to
an actual xenstored implementation, but in the fullness of time it would
be nice to have a fully single-tenant "virtual" xenstore within qemu.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 hw/i386/kvm/xen_xenstore.c | 223 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 220 insertions(+), 3 deletions(-)

diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
index bb3346f4e3..6369e29f59 100644
--- a/hw/i386/kvm/xen_xenstore.c
+++ b/hw/i386/kvm/xen_xenstore.c
@@ -188,18 +188,235 @@ uint16_t xen_xenstore_get_port(void)
     return s->guest_port;
 }
 
+static bool req_pending(XenXenstoreState *s)
+{
+    struct xsd_sockmsg *req = (struct xsd_sockmsg *)s->req_data;
+
+    return s->req_offset == XENSTORE_HEADER_SIZE + req->len;
+}
+
+static void reset_req(XenXenstoreState *s)
+{
+    memset(s->req_data, 0, sizeof(s->req_data));
+    s->req_offset = 0;
+}
+
+static void reset_rsp(XenXenstoreState *s)
+{
+    s->rsp_pending = false;
+
+    memset(s->rsp_data, 0, sizeof(s->rsp_data));
+    s->rsp_offset = 0;
+}
+
+static void process_req(XenXenstoreState *s)
+{
+    struct xsd_sockmsg *req = (struct xsd_sockmsg *)s->req_data;
+    struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
+    const char enosys[] = "ENOSYS";
+
+    assert(req_pending(s));
+	assert(!s->rsp_pending);
+
+    rsp->type = XS_ERROR;
+    rsp->req_id = req->req_id;
+    rsp->tx_id = req->tx_id;
+    rsp->len = sizeof(enosys);
+    memcpy((void *)&rsp[1], enosys, sizeof(enosys));
+
+    s->rsp_pending = true;
+    reset_req(s);
+}
+
+static unsigned int copy_from_ring(XenXenstoreState *s, uint8_t *ptr, unsigned int len)
+{
+    if (!len)
+        return 0;
+
+    XENSTORE_RING_IDX prod = qatomic_read(&s->xs->req_prod);
+    XENSTORE_RING_IDX cons = qatomic_read(&s->xs->req_cons);
+    unsigned int copied = 0;
+
+    smp_mb();
+
+    while (len) {
+        unsigned int avail = prod - cons;
+        unsigned int offset = MASK_XENSTORE_IDX(cons);
+        unsigned int copylen = avail;
+
+        if (avail > XENSTORE_RING_SIZE) {
+            error_report("XenStore ring handling error");
+            s->fatal_error = true;
+            break;
+        } else if (avail == 0)
+            break;
+
+        if (copylen > len) {
+            copylen = len;
+        }
+        if (copylen > XENSTORE_RING_SIZE - offset) {
+            copylen = XENSTORE_RING_SIZE - offset;
+        }
+
+        memcpy(ptr, &s->xs->req[offset], copylen);
+        copied += copylen;
+
+        ptr += copylen;
+        len -= copylen;
+
+        cons += copylen;
+    }
+
+    smp_mb();
+
+    qatomic_set(&s->xs->req_cons, cons);
+
+    return copied;
+}
+
+static unsigned int copy_to_ring(XenXenstoreState *s, uint8_t *ptr, unsigned int len)
+{
+    if (!len)
+        return 0;
+
+    XENSTORE_RING_IDX cons = qatomic_read(&s->xs->rsp_cons);
+    XENSTORE_RING_IDX prod = qatomic_read(&s->xs->rsp_prod);
+    unsigned int copied = 0;
+
+    smp_mb();
+
+    while (len) {
+        unsigned int avail = cons + XENSTORE_RING_SIZE - prod;
+        unsigned int offset = MASK_XENSTORE_IDX(prod);
+        unsigned int copylen = len;
+
+        if (avail > XENSTORE_RING_SIZE) {
+            error_report("XenStore ring handling error");
+            s->fatal_error = true;
+            break;
+        } else if (avail == 0)
+            break;
+
+        if (copylen > avail) {
+            copylen = avail;
+        }
+        if (copylen > XENSTORE_RING_SIZE - offset) {
+            copylen = XENSTORE_RING_SIZE - offset;
+        }
+
+
+        memcpy(&s->xs->rsp[offset], ptr, copylen);
+        copied += copylen;
+
+        ptr += copylen;
+        len -= copylen;
+
+        prod += copylen;
+    }
+
+    smp_mb();
+
+    qatomic_set(&s->xs->rsp_prod, prod);
+
+    return copied;
+}
+
+static unsigned int get_req(XenXenstoreState *s)
+{
+    unsigned int copied = 0;
+
+    if (s->fatal_error)
+        return 0;
+
+    assert(!req_pending(s));
+
+    if (s->req_offset < XENSTORE_HEADER_SIZE) {
+        void *ptr = s->req_data + s->req_offset;
+        unsigned int len = XENSTORE_HEADER_SIZE;
+        unsigned int copylen = copy_from_ring(s, ptr, len);
+
+        copied += copylen;
+        s->req_offset += copylen;
+    }
+
+    if (s->req_offset >= XENSTORE_HEADER_SIZE) {
+        struct xsd_sockmsg *req = (struct xsd_sockmsg *)s->req_data;
+
+        if (req->len > (uint32_t)XENSTORE_PAYLOAD_MAX) {
+            error_report("Illegal XenStore request");
+            s->fatal_error = true;
+            return 0;
+        }
+
+        void *ptr = s->req_data + s->req_offset;
+        unsigned int len = XENSTORE_HEADER_SIZE + req->len - s->req_offset;
+        unsigned int copylen = copy_from_ring(s, ptr, len);
+
+        copied += copylen;
+        s->req_offset += copylen;
+    }
+
+    return copied;
+}
+
+static unsigned int put_rsp(XenXenstoreState *s)
+{
+    if (s->fatal_error)
+        return 0;
+
+    assert(s->rsp_pending);
+
+    struct xsd_sockmsg *rsp = (struct xsd_sockmsg *)s->rsp_data;
+    assert(s->rsp_offset < XENSTORE_HEADER_SIZE + rsp->len);
+
+    void *ptr = s->rsp_data + s->rsp_offset;
+    unsigned int len = XENSTORE_HEADER_SIZE + rsp->len - s->rsp_offset;
+    unsigned int copylen = copy_to_ring(s, ptr, len);
+
+    s->rsp_offset += copylen;
+
+    /* Have we produced a complete response? */
+    if (s->rsp_offset == XENSTORE_HEADER_SIZE + rsp->len)
+        reset_rsp(s);
+
+    return copylen;
+}
+
 static void xen_xenstore_event(void *opaque)
 {
     XenXenstoreState *s = opaque;
     evtchn_port_t port = xen_be_evtchn_pending(s->eh);
+    unsigned int copied_to, copied_from;
+    bool processed, notify = false;
+
     if (port != s->be_port) {
         return;
     }
-    printf("xenstore event\n");
+
     /* We know this is a no-op. */
     xen_be_evtchn_unmask(s->eh, port);
-    qemu_hexdump(stdout, "", s->xs, sizeof(*s->xs));
-    xen_be_evtchn_notify(s->eh, s->be_port);
+
+    do {
+        copied_to = copied_from = 0;
+        processed = false;
+
+        if (s->rsp_pending)
+            copied_to = put_rsp(s);
+
+        if (!req_pending(s))
+            copied_from = get_req(s);
+
+        if (req_pending(s) && !s->rsp_pending) {
+            process_req(s);
+            processed = true;
+        }
+
+        notify |= copied_to || copied_from;
+    } while (copied_to || copied_from || processed);
+
+    if (notify) {
+        xen_be_evtchn_notify(s->eh, s->be_port);
+    }
 }
 
 static void alloc_guest_port(XenXenstoreState *s)
-- 
2.35.3