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>

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 86cac3e..6c8a238 100644 (file)
--- 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