/*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
* controls and communicates with the Guest. For example, the first write will
- * tell us the memory size, pagetable, entry point and kernel address offset.
- * A read will run the Guest until a signal is pending (-EINTR), or the Guest
- * does a DMA out to the Launcher. Writes are also used to get a DMA buffer
- * registered by the Guest and to send the Guest an interrupt. :*/
+ * tell us the Guest's memory layout and entry point. A read will run the
+ * Guest until something happens, such as a signal or the Guest doing a NOTIFY
+ * out to the Launcher.
+:*/
#include <linux/uaccess.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/eventfd.h>
+#include <linux/file.h>
#include "lg.h"
-/*L:030 setup_regs() doesn't really belong in this file, but it gives us an
- * early glimpse deeper into the Host so it's worth having here.
+/*L:056
+ * Before we move on, let's jump ahead and look at what the kernel does when
+ * it needs to look up the eventfds. That will complete our picture of how we
+ * use RCU.
*
- * Most of the Guest's registers are left alone: we used get_zeroed_page() to
- * allocate the structure, so they will be 0. */
-static void setup_regs(struct lguest_regs *regs, unsigned long start)
+ * The notification value is in cpu->pending_notify: we return true if it went
+ * to an eventfd.
+ */
+bool send_notify_to_eventfd(struct lg_cpu *cpu)
{
- /* There are four "segment" registers which the Guest needs to boot:
- * The "code segment" register (cs) refers to the kernel code segment
- * __KERNEL_CS, and the "data", "extra" and "stack" segment registers
- * refer to the kernel data segment __KERNEL_DS.
+ unsigned int i;
+ struct lg_eventfd_map *map;
+
+ /*
+ * This "rcu_read_lock()" helps track when someone is still looking at
+ * the (RCU-using) eventfds array. It's not actually a lock at all;
+ * indeed it's a noop in many configurations. (You didn't expect me to
+ * explain all the RCU secrets here, did you?)
+ */
+ rcu_read_lock();
+ /*
+ * rcu_dereference is the counter-side of rcu_assign_pointer(); it
+ * makes sure we don't access the memory pointed to by
+ * cpu->lg->eventfds before cpu->lg->eventfds is set. Sounds crazy,
+ * but Alpha allows this! Paul McKenney points out that a really
+ * aggressive compiler could have the same effect:
+ * http://lists.ozlabs.org/pipermail/lguest/2009-July/001560.html
*
- * The privilege level is packed into the lower bits. The Guest runs
- * at privilege level 1 (GUEST_PL).*/
- regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
- regs->cs = __KERNEL_CS|GUEST_PL;
-
- /* The "eflags" register contains miscellaneous flags. Bit 1 (0x002)
- * is supposed to always be "1". Bit 9 (0x200) controls whether
- * interrupts are enabled. We always leave interrupts enabled while
- * running the Guest. */
- regs->eflags = 0x202;
-
- /* The "Extended Instruction Pointer" register says where the Guest is
- * running. */
- regs->eip = start;
-
- /* %esi points to our boot information, at physical address 0, so don't
- * touch it. */
+ * So play safe, use rcu_dereference to get the rcu-protected pointer:
+ */
+ map = rcu_dereference(cpu->lg->eventfds);
+ /*
+ * Simple array search: even if they add an eventfd while we do this,
+ * we'll continue to use the old array and just won't see the new one.
+ */
+ for (i = 0; i < map->num; i++) {
+ if (map->map[i].addr == cpu->pending_notify) {
+ eventfd_signal(map->map[i].event, 1);
+ cpu->pending_notify = 0;
+ break;
+ }
+ }
+ /* We're done with the rcu-protected variable cpu->lg->eventfds. */
+ rcu_read_unlock();
+
+ /* If we cleared the notification, it's because we found a match. */
+ return cpu->pending_notify == 0;
}
-/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a
- * DMA buffer. This is done by writing LHREQ_GETDMA and the key to
- * /dev/lguest. */
-static long user_get_dma(struct lguest *lg, const u32 __user *input)
+/*L:055
+ * One of the more tricksy tricks in the Linux Kernel is a technique called
+ * Read Copy Update. Since one point of lguest is to teach lguest journeyers
+ * about kernel coding, I use it here. (In case you're curious, other purposes
+ * include learning about virtualization and instilling a deep appreciation for
+ * simplicity and puppies).
+ *
+ * We keep a simple array which maps LHCALL_NOTIFY values to eventfds, but we
+ * add new eventfds without ever blocking readers from accessing the array.
+ * The current Launcher only does this during boot, so that never happens. But
+ * Read Copy Update is cool, and adding a lock risks damaging even more puppies
+ * than this code does.
+ *
+ * We allocate a brand new one-larger array, copy the old one and add our new
+ * element. Then we make the lg eventfd pointer point to the new array.
+ * That's the easy part: now we need to free the old one, but we need to make
+ * sure no slow CPU somewhere is still looking at it. That's what
+ * synchronize_rcu does for us: waits until every CPU has indicated that it has
+ * moved on to know it's no longer using the old one.
+ *
+ * If that's unclear, see http://en.wikipedia.org/wiki/Read-copy-update.
+ */
+static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
{
- unsigned long key, udma, irq;
+ struct lg_eventfd_map *new, *old = lg->eventfds;
- /* Fetch the key they wrote to us. */
- if (get_user(key, input) != 0)
- return -EFAULT;
- /* Look for a free Guest DMA buffer bound to that key. */
- udma = get_dma_buffer(lg, key, &irq);
- if (!udma)
- return -ENOENT;
-
- /* We need to tell the Launcher what interrupt the Guest expects after
- * the buffer is filled. We stash it in udma->used_len. */
- lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);
-
- /* The (guest-physical) address of the DMA buffer is returned from
- * the write(). */
- return udma;
+ /*
+ * We don't allow notifications on value 0 anyway (pending_notify of
+ * 0 means "nothing pending").
+ */
+ if (!addr)
+ return -EINVAL;
+
+ /*
+ * Replace the old array with the new one, carefully: others can
+ * be accessing it at the same time.
+ */
+ new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
+ GFP_KERNEL);
+ if (!new)
+ return -ENOMEM;
+
+ /* First make identical copy. */
+ memcpy(new->map, old->map, sizeof(old->map[0]) * old->num);
+ new->num = old->num;
+
+ /* Now append new entry. */
+ new->map[new->num].addr = addr;
+ new->map[new->num].event = eventfd_ctx_fdget(fd);
+ if (IS_ERR(new->map[new->num].event)) {
+ int err = PTR_ERR(new->map[new->num].event);
+ kfree(new);
+ return err;
+ }
+ new->num++;
+
+ /*
+ * Now put new one in place: rcu_assign_pointer() is a fancy way of
+ * doing "lg->eventfds = new", but it uses memory barriers to make
+ * absolutely sure that the contents of "new" written above is nailed
+ * down before we actually do the assignment.
+ *
+ * We have to think about these kinds of things when we're operating on
+ * live data without locks.
+ */
+ rcu_assign_pointer(lg->eventfds, new);
+
+ /*
+ * We're not in a big hurry. Wait until noone's looking at old
+ * version, then free it.
+ */
+ synchronize_rcu();
+ kfree(old);
+
+ return 0;
}
-/*L:315 To force the Guest to stop running and return to the Launcher, the
- * Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest. The
- * Launcher then writes LHREQ_BREAK and "0" to release the Waker. */
-static int break_guest_out(struct lguest *lg, const u32 __user *input)
+/*L:052
+ * Receiving notifications from the Guest is usually done by attaching a
+ * particular LHCALL_NOTIFY value to an event filedescriptor. The eventfd will
+ * become readable when the Guest does an LHCALL_NOTIFY with that value.
+ *
+ * This is really convenient for processing each virtqueue in a separate
+ * thread.
+ */
+static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
{
- unsigned long on;
+ unsigned long addr, fd;
+ int err;
- /* Fetch whether they're turning break on or off.. */
- if (get_user(on, input) != 0)
+ if (get_user(addr, input) != 0)
+ return -EFAULT;
+ input++;
+ if (get_user(fd, input) != 0)
return -EFAULT;
- if (on) {
- lg->break_out = 1;
- /* Pop it out (may be running on different CPU) */
- wake_up_process(lg->tsk);
- /* Wait for them to reset it */
- return wait_event_interruptible(lg->break_wq, !lg->break_out);
- } else {
- lg->break_out = 0;
- wake_up(&lg->break_wq);
- return 0;
- }
+ /*
+ * Just make sure two callers don't add eventfds at once. We really
+ * only need to lock against callers adding to the same Guest, so using
+ * the Big Lguest Lock is overkill. But this is setup, not a fast path.
+ */
+ mutex_lock(&lguest_lock);
+ err = add_eventfd(lg, addr, fd);
+ mutex_unlock(&lguest_lock);
+
+ return err;
}
-/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
- * number to /dev/lguest. */
-static int user_send_irq(struct lguest *lg, const u32 __user *input)
+/*L:050
+ * Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
+ * number to /dev/lguest.
+ */
+static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
{
- u32 irq;
+ unsigned long irq;
if (get_user(irq, input) != 0)
return -EFAULT;
if (irq >= LGUEST_IRQS)
return -EINVAL;
- /* Next time the Guest runs, the core code will see if it can deliver
- * this interrupt. */
- set_bit(irq, lg->irqs_pending);
+
+ /*
+ * Next time the Guest runs, the core code will see if it can deliver
+ * this interrupt.
+ */
+ set_interrupt(cpu, irq);
return 0;
}
-/*L:040 Once our Guest is initialized, the Launcher makes it run by reading
- * from /dev/lguest. */
+/*L:040
+ * Once our Guest is initialized, the Launcher makes it run by reading
+ * from /dev/lguest.
+ */
static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
{
struct lguest *lg = file->private_data;
+ struct lg_cpu *cpu;
+ unsigned int cpu_id = *o;
/* You must write LHREQ_INITIALIZE first! */
if (!lg)
return -EINVAL;
- /* If you're not the task which owns the guest, go away. */
- if (current != lg->tsk)
+ /* Watch out for arbitrary vcpu indexes! */
+ if (cpu_id >= lg->nr_cpus)
+ return -EINVAL;
+
+ cpu = &lg->cpus[cpu_id];
+
+ /* If you're not the task which owns the Guest, go away. */
+ 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;
return len;
}
- /* If we returned from read() last time because the Guest sent DMA,
- * clear the flag. */
- if (lg->dma_is_pending)
- lg->dma_is_pending = 0;
+ /*
+ * If we returned from read() last time because the Guest sent I/O,
+ * clear the flag.
+ */
+ if (cpu->pending_notify)
+ cpu->pending_notify = 0;
/* Run the Guest until something interesting happens. */
- return run_guest(lg, (unsigned long __user *)user);
+ return run_guest(cpu, (unsigned long __user *)user);
}
-/*L:020 The initialization write supplies 4 32-bit values (in addition to the
- * 32-bit LHREQ_INITIALIZE value). These are:
+/*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 >= ARRAY_SIZE(cpu->lg->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
+ * to the Guest and we can only grant it access to whole pages.
+ */
+ cpu->regs_page = get_zeroed_page(GFP_KERNEL);
+ if (!cpu->regs_page)
+ return -ENOMEM;
+
+ /* We actually put the registers at the bottom of the page. */
+ cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
+
+ /*
+ * Now we initialize the Guest's registers, handing it the start
+ * address.
+ */
+ lguest_arch_setup_regs(cpu, start_ip);
+
+ /*
+ * We keep a pointer to the Launcher task (ie. current task) for when
+ * 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
+ * the Launcher dies we need to clean it up. If we don't keep a
+ * reference, it is destroyed before close() is called.
+ */
+ cpu->mm = get_task_mm(cpu->tsk);
+
+ /*
+ * We remember which CPU's pages this Guest used last, for optimization
+ * when the same Guest runs on the same CPU twice.
+ */
+ cpu->last_pages = NULL;
+
+ /* No error == success. */
+ return 0;
+}
+
+/*L:020
+ * The initialization write supplies 3 pointer sized (32 or 64 bit) values (in
+ * addition to the LHREQ_INITIALIZE value). These are:
*
- * pfnlimit: The highest (Guest-physical) page number the Guest should be
- * allowed to access. The Launcher has to live in Guest memory, so it sets
- * this to ensure the Guest can't reach it.
+ * base: The start of the Guest-physical memory inside the Launcher memory.
*
- * pgdir: The (Guest-physical) address of the top of the initial Guest
- * pagetables (which are set up by the Launcher).
+ * pfnlimit: The highest (Guest-physical) page number the Guest should be
+ * allowed to access. The Guest memory lives inside the Launcher, so it sets
+ * this to ensure the Guest can only reach its own memory.
*
* start: The first instruction to execute ("eip" in x86-speak).
- *
- * page_offset: The PAGE_OFFSET constant in the Guest kernel. We should
- * probably wean the code off this, but it's a very useful constant! Any
- * address above this is within the Guest kernel, and any kernel address can
- * quickly converted from physical to virtual by adding PAGE_OFFSET. It's
- * 0xC0000000 (3G) by default, but it's configurable at kernel build time.
*/
-static int initialize(struct file *file, const u32 __user *input)
+static int initialize(struct file *file, const unsigned long __user *input)
{
- /* "struct lguest" contains everything we (the Host) know about a
- * Guest. */
+ /* "struct lguest" contains all we (the Host) know about a Guest. */
struct lguest *lg;
- int err, i;
- u32 args[4];
+ int err;
+ unsigned long args[3];
- /* We grab the Big Lguest lock, which protects the global array
- * "lguests" and multiple simultaneous initializations. */
+ /*
+ * We grab the Big Lguest lock, which protects against multiple
+ * simultaneous initializations.
+ */
mutex_lock(&lguest_lock);
/* You can't initialize twice! Close the device and start again... */
if (file->private_data) {
goto unlock;
}
- /* Find an unused guest. */
- i = find_free_guest();
- if (i < 0) {
- err = -ENOSPC;
+ lg = kzalloc(sizeof(*lg), GFP_KERNEL);
+ if (!lg) {
+ err = -ENOMEM;
goto unlock;
}
- /* OK, we have an index into the "lguest" array: "lg" is a convenient
- * pointer. */
- lg = &lguests[i];
- /* Populate the easy fields of our "struct lguest" */
- lg->guestid = i;
- lg->pfn_limit = args[0];
- lg->page_offset = args[3];
-
- /* We need a complete page for the Guest registers: they are accessible
- * to the Guest and we can only grant it access to whole pages. */
- lg->regs_page = get_zeroed_page(GFP_KERNEL);
- if (!lg->regs_page) {
+ lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL);
+ if (!lg->eventfds) {
err = -ENOMEM;
- goto release_guest;
+ goto free_lg;
}
- /* We actually put the registers at the bottom of the page. */
- lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);
-
- /* Initialize the Guest's shadow page tables, using the toplevel
- * address the Launcher gave us. This allocates memory, so can
- * fail. */
- err = init_guest_pagetable(lg, args[1]);
- if (err)
- goto free_regs;
+ lg->eventfds->num = 0;
- /* Now we initialize the Guest's registers, handing it the start
- * address. */
- setup_regs(lg->regs, args[2]);
-
- /* There are a couple of GDT entries the Guest expects when first
- * booting. */
- setup_guest_gdt(lg);
-
- /* The timer for lguest's clock needs initialization. */
- init_clockdev(lg);
-
- /* We keep a pointer to the Launcher task (ie. current task) for when
- * other Guests want to wake this one (inter-Guest I/O). */
- lg->tsk = current;
- /* We need to keep a pointer to the Launcher's memory map, because if
- * the Launcher dies we need to clean it up. If we don't keep a
- * reference, it is destroyed before close() is called. */
- lg->mm = get_task_mm(lg->tsk);
+ /* Populate the easy fields of our "struct lguest" */
+ lg->mem_base = (void __user *)args[0];
+ lg->pfn_limit = args[1];
- /* Initialize the queue for the waker to wait on */
- init_waitqueue_head(&lg->break_wq);
+ /* This is the first cpu (cpu 0) and it will start booting at args[2] */
+ err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
+ if (err)
+ goto free_eventfds;
- /* We remember which CPU's pages this Guest used last, for optimization
- * when the same Guest runs on the same CPU twice. */
- lg->last_pages = NULL;
+ /*
+ * Initialize the Guest's shadow page tables, using the toplevel
+ * address the Launcher gave us. This allocates memory, so can fail.
+ */
+ err = init_guest_pagetable(lg);
+ if (err)
+ goto free_regs;
/* We keep our "struct lguest" in the file's private_data. */
file->private_data = lg;
return sizeof(args);
free_regs:
- free_page(lg->regs_page);
-release_guest:
- memset(lg, 0, sizeof(*lg));
+ /* FIXME: This should be in free_vcpu */
+ free_page(lg->cpus[0].regs_page);
+free_eventfds:
+ kfree(lg->eventfds);
+free_lg:
+ kfree(lg);
unlock:
mutex_unlock(&lguest_lock);
return err;
}
-/*L:010 The first operation the Launcher does must be a write. All writes
- * start with a 32 bit number: for the first write this must be
+/*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 get DMA buffers and send interrupts. */
-static ssize_t write(struct file *file, const char __user *input,
+ * writes of other values to send interrupts or set up receipt of notifications.
+ *
+ * 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
- * file private data. */
+ /*
+ * Once the Guest is initialized, we hold the "struct lguest" in the
+ * file private data.
+ */
struct lguest *lg = file->private_data;
- u32 req;
+ const unsigned long __user *input = (const unsigned long __user *)in;
+ unsigned long req;
+ 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 += sizeof(req);
+ input++;
/* If you haven't initialized, you must do that first. */
- if (req != LHREQ_INITIALIZE && !lg)
- return -EINVAL;
-
- /* Once the Guest is dead, all you can do is read() why it died. */
- if (lg && lg->dead)
- return -ENOENT;
-
- /* If you're not the task which owns the Guest, you can only break */
- if (lg && current != lg->tsk && req != LHREQ_BREAK)
- return -EPERM;
+ if (req != LHREQ_INITIALIZE) {
+ if (!lg || (cpu_id >= lg->nr_cpus))
+ return -EINVAL;
+ cpu = &lg->cpus[cpu_id];
+
+ /* Once the Guest is dead, you can only read() why it died. */
+ if (lg->dead)
+ return -ENOENT;
+ }
switch (req) {
case LHREQ_INITIALIZE:
- return initialize(file, (const u32 __user *)input);
- case LHREQ_GETDMA:
- return user_get_dma(lg, (const u32 __user *)input);
+ return initialize(file, input);
case LHREQ_IRQ:
- return user_send_irq(lg, (const u32 __user *)input);
- case LHREQ_BREAK:
- return break_guest_out(lg, (const u32 __user *)input);
+ return user_send_irq(cpu, input);
+ case LHREQ_EVENTFD:
+ return attach_eventfd(lg, input);
default:
return -EINVAL;
}
}
-/*L:060 The final piece of interface code is the close() routine. It reverses
+/*L:060
+ * The final piece of interface code is the close() routine. It reverses
* everything done in initialize(). This is usually called because the
* Launcher exited.
*
* Note that the close routine returns 0 or a negative error number: it can't
* really fail, but it can whine. I blame Sun for this wart, and K&R C for
- * letting them do it. :*/
+ * letting them do it.
+:*/
static int close(struct inode *inode, struct file *file)
{
struct lguest *lg = file->private_data;
+ unsigned int i;
/* If we never successfully initialized, there's nothing to clean up */
if (!lg)
return 0;
- /* We need the big lock, to protect from inter-guest I/O and other
- * Launchers initializing guests. */
+ /*
+ * We need the big lock, to protect from inter-guest I/O and other
+ * Launchers initializing guests.
+ */
mutex_lock(&lguest_lock);
- /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
- hrtimer_cancel(&lg->hrt);
- /* Free any DMA buffers the Guest had bound. */
- release_all_dma(lg);
+
/* Free up the shadow page tables for the Guest. */
free_guest_pagetable(lg);
- /* Now all the memory cleanups are done, it's safe to release the
- * Launcher's memory management structure. */
- mmput(lg->mm);
- /* If lg->dead doesn't contain an error code it will be NULL or a
- * kmalloc()ed string, either of which is ok to hand to kfree(). */
+
+ for (i = 0; i < lg->nr_cpus; i++) {
+ /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
+ hrtimer_cancel(&lg->cpus[i].hrt);
+ /* We can free up the register page we allocated. */
+ free_page(lg->cpus[i].regs_page);
+ /*
+ * Now all the memory cleanups are done, it's safe to release
+ * the Launcher's memory management structure.
+ */
+ mmput(lg->cpus[i].mm);
+ }
+
+ /* Release any eventfds they registered. */
+ for (i = 0; i < lg->eventfds->num; i++)
+ eventfd_ctx_put(lg->eventfds->map[i].event);
+ kfree(lg->eventfds);
+
+ /*
+ * If lg->dead doesn't contain an error code it will be NULL or a
+ * kmalloc()ed string, either of which is ok to hand to kfree().
+ */
if (!IS_ERR(lg->dead))
kfree(lg->dead);
- /* We can free up the register page we allocated. */
- free_page(lg->regs_page);
- /* We clear the entire structure, which also marks it as free for the
- * next user. */
- memset(lg, 0, sizeof(*lg));
+ /* Free the memory allocated to the lguest_struct */
+ kfree(lg);
/* Release lock and exit. */
mutex_unlock(&lguest_lock);
* The Launcher is the Host userspace program which sets up, runs and services
* the Guest. In fact, many comments in the Drivers which refer to "the Host"
* doing things are inaccurate: the Launcher does all the device handling for
- * the Guest. The Guest can't tell what's done by the the Launcher and what by
- * the Host.
+ * the Guest, but the Guest can't know that.
*
* Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
* shall see more of that later.
*
* We begin our understanding with the Host kernel interface which the Launcher
* uses: reading and writing a character device called /dev/lguest. All the
- * work happens in the read(), write() and close() routines: */
-static struct file_operations lguest_fops = {
+ * work happens in the read(), write() and close() routines:
+ */
+static const struct file_operations lguest_fops = {
.owner = THIS_MODULE,
.release = close,
.write = write,
.read = read,
};
-/* This is a textbook example of a "misc" character device. Populate a "struct
- * miscdevice" and register it with misc_register(). */
+/*
+ * This is a textbook example of a "misc" character device. Populate a "struct
+ * miscdevice" and register it with misc_register().
+ */
static struct miscdevice lguest_dev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "lguest",
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