lguest: comment documentation update.
Took some cycles to re-read the Lguest Journey end-to-end, fix some
rot and tighten some phrases.
Only comments change. No new jokes, but a couple of recycled old jokes.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 2221485..564e425 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -73,7 +73,7 @@
if (current != cpu->tsk)
return -EPERM;
- /* If the guest is already dead, we indicate why */
+ /* If the Guest is already dead, we indicate why */
if (lg->dead) {
size_t len;
@@ -88,7 +88,7 @@
return len;
}
- /* If we returned from read() last time because the Guest notified,
+ /* If we returned from read() last time because the Guest sent I/O,
* clear the flag. */
if (cpu->pending_notify)
cpu->pending_notify = 0;
@@ -97,14 +97,20 @@
return run_guest(cpu, (unsigned long __user *)user);
}
+/*L:025 This actually initializes a CPU. For the moment, a Guest is only
+ * uniprocessor, so "id" is always 0. */
static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
{
+ /* We have a limited number the number of CPUs in the lguest struct. */
if (id >= NR_CPUS)
return -EINVAL;
+ /* Set up this CPU's id, and pointer back to the lguest struct. */
cpu->id = id;
cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
cpu->lg->nr_cpus++;
+
+ /* Each CPU has a timer it can set. */
init_clockdev(cpu);
/* We need a complete page for the Guest registers: they are accessible
@@ -120,11 +126,11 @@
* address. */
lguest_arch_setup_regs(cpu, start_ip);
- /* Initialize the queue for the waker to wait on */
+ /* Initialize the queue for the Waker to wait on */
init_waitqueue_head(&cpu->break_wq);
/* We keep a pointer to the Launcher task (ie. current task) for when
- * other Guests want to wake this one (inter-Guest I/O). */
+ * other Guests want to wake this one (eg. console input). */
cpu->tsk = current;
/* We need to keep a pointer to the Launcher's memory map, because if
@@ -136,6 +142,7 @@
* when the same Guest runs on the same CPU twice. */
cpu->last_pages = NULL;
+ /* No error == success. */
return 0;
}
@@ -185,14 +192,13 @@
lg->mem_base = (void __user *)(long)args[0];
lg->pfn_limit = args[1];
- /* This is the first cpu */
+ /* This is the first cpu (cpu 0) and it will start booting at args[3] */
err = lg_cpu_start(&lg->cpus[0], 0, args[3]);
if (err)
goto release_guest;
/* Initialize the Guest's shadow page tables, using the toplevel
- * address the Launcher gave us. This allocates memory, so can
- * fail. */
+ * address the Launcher gave us. This allocates memory, so can fail. */
err = init_guest_pagetable(lg, args[2]);
if (err)
goto free_regs;
@@ -218,11 +224,16 @@
/*L:010 The first operation the Launcher does must be a write. All writes
* start with an unsigned long number: for the first write this must be
* LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use
- * writes of other values to send interrupts. */
+ * writes of other values to send interrupts.
+ *
+ * Note that we overload the "offset" in the /dev/lguest file to indicate what
+ * CPU number we're dealing with. Currently this is always 0, since we only
+ * support uniprocessor Guests, but you can see the beginnings of SMP support
+ * here. */
static ssize_t write(struct file *file, const char __user *in,
size_t size, loff_t *off)
{
- /* Once the guest is initialized, we hold the "struct lguest" in the
+ /* Once the Guest is initialized, we hold the "struct lguest" in the
* file private data. */
struct lguest *lg = file->private_data;
const unsigned long __user *input = (const unsigned long __user *)in;
@@ -230,6 +241,7 @@
struct lg_cpu *uninitialized_var(cpu);
unsigned int cpu_id = *off;
+ /* The first value tells us what this request is. */
if (get_user(req, input) != 0)
return -EFAULT;
input++;