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>

1 files changed, 21 insertions, 9 deletions

diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 2221485b0773..564e425d71dd 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -73,7 +73,7 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
         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 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
                 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 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
         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 @@ static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
          * 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 @@ static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
          * when the same Guest runs on the same CPU twice. */
         cpu->last_pages = NULL;
 
+        /* No error == success. */
         return 0;
 }
 
@@ -185,14 +192,13 @@ static int initialize(struct file *file, const unsigned long __user *input)
         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 @@ unlock:
 /*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 @@ static ssize_t write(struct file *file, const char __user *in,
         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++;