lguest: adapt launcher to per-cpuness

This patch makes uses of pread() and pwrite() in lguest launcher
to communicate the vcpu id to the lguest driver. The id is kept in
a thread variable, which means we'll span in the future, vcpus as
threads. But right now, only the infrastructure is out there.

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 13 insertions, 4 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 86cac3e622ab..6c8a2386cd50 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -79,6 +79,9 @@ static void *guest_base;
 /* The maximum guest physical address allowed, and maximum possible. */
 static unsigned long guest_limit, guest_max;
 
+/* a per-cpu variable indicating whose vcpu is currently running */
+static unsigned int __thread cpu_id;
+
 /* This is our list of devices. */
 struct device_list
 {
@@ -557,7 +560,7 @@ static void wake_parent(int pipefd, int lguest_fd)
                         else
                                 FD_CLR(-fd - 1, &devices.infds);
                 } else /* Send LHREQ_BREAK command. */
-                        write(lguest_fd, args, sizeof(args));
+                        pwrite(lguest_fd, args, sizeof(args), cpu_id);
         }
 }
 
@@ -1530,7 +1533,8 @@ static void __attribute__((noreturn)) run_guest(int lguest_fd)
                 int readval;
 
                 /* We read from the /dev/lguest device to run the Guest. */
-                readval = read(lguest_fd, &notify_addr, sizeof(notify_addr));
+                readval = pread(lguest_fd, &notify_addr,
+                                sizeof(notify_addr), cpu_id);
 
                 /* One unsigned long means the Guest did HCALL_NOTIFY */
                 if (readval == sizeof(notify_addr)) {
@@ -1540,7 +1544,7 @@ static void __attribute__((noreturn)) run_guest(int lguest_fd)
                 /* ENOENT means the Guest died.  Reading tells us why. */
                 } else if (errno == ENOENT) {
                         char reason[1024] = { 0 };
-                        read(lguest_fd, reason, sizeof(reason)-1);
+                        pread(lguest_fd, reason, sizeof(reason)-1, cpu_id);
                         errx(1, "%s", reason);
                 /* ERESTART means that we need to reboot the guest */
                 } else if (errno == ERESTART) {
@@ -1550,9 +1554,13 @@ static void __attribute__((noreturn)) run_guest(int lguest_fd)
                 } else if (errno != EAGAIN)
                         err(1, "Running guest failed");
 
+                /* Only service input on thread for CPU 0. */
+                if (cpu_id != 0)
+                        continue;
+
                 /* Service input, then unset the BREAK to release the Waker. */
                 handle_input(lguest_fd);
-                if (write(lguest_fd, args, sizeof(args)) < 0)
+                if (pwrite(lguest_fd, args, sizeof(args), cpu_id) < 0)
                         err(1, "Resetting break");
         }
 }
@@ -1610,6 +1618,7 @@ int main(int argc, char *argv[])
         devices.lastdev = &devices.dev;
         devices.next_irq = 1;
 
+        cpu_id = 0;
         /* We need to know how much memory so we can set up the device
          * descriptor and memory pages for the devices as we parse the command
          * line.  So we quickly look through the arguments to find the amount