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Date: Tue, 9 Feb 2021 09:52:30 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Adrian Catangiu <acatan@...zon.com>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
qemu-devel@...gnu.org, kvm@...r.kernel.org,
linux-s390@...r.kernel.org, gregkh@...uxfoundation.org,
graf@...zon.com, rdunlap@...radead.org, arnd@...db.de,
ebiederm@...ssion.com, rppt@...nel.org, 0x7f454c46@...il.com,
borntraeger@...ibm.com, Jason@...c4.com, jannh@...gle.com,
w@....eu, colmmacc@...zon.com, luto@...nel.org, tytso@....edu,
ebiggers@...nel.org, dwmw@...zon.co.uk, bonzini@....org,
sblbir@...zon.com, raduweis@...zon.com, corbet@....net,
mhocko@...nel.org, rafael@...nel.org, pavel@....cz,
mpe@...erman.id.au, areber@...hat.com, ovzxemul@...il.com,
avagin@...il.com, ptikhomirov@...tuozzo.com, gil@...l.com,
asmehra@...hat.com, dgunigun@...hat.com, vijaysun@...ibm.com,
oridgar@...il.com, ghammer@...hat.com
Subject: Re: [PATCH v5 1/2] drivers/misc: sysgenid: add system generation id
driver
On Mon, Feb 01, 2021 at 07:24:53PM +0200, Adrian Catangiu wrote:
> - Background and problem
>
> The System Generation ID feature is required in virtualized or
> containerized environments by applications that work with local copies
> or caches of world-unique data such as random values, uuids,
> monotonically increasing counters, etc.
> Such applications can be negatively affected by VM or container
> snapshotting when the VM or container is either cloned or returned to
> an earlier point in time.
>
> Furthermore, simply finding out about a system generation change is
> only the starting point of a process to renew internal states of
> possibly multiple applications across the system. This process could
> benefit from a driver that provides an interface through which
> orchestration can be easily done.
>
> - Solution
>
> The System Generation ID is a simple concept meant to alleviate the
> issue by providing a monotonically increasing u32 counter that changes
> each time the VM or container is restored from a snapshot.
>
> The `sysgenid` driver exposes a monotonic incremental System Generation
> u32 counter via a char-dev FS interface that provides sync and async
> SysGen counter updates notifications. It also provides SysGen counter
> retrieval and confirmation mechanisms.
>
> The counter starts from zero when the driver is initialized and
> monotonically increments every time the system generation changes.
>
> The `sysgenid` driver exports the `void sysgenid_bump_generation()`
> symbol which can be used by backend drivers to drive system generation
> changes based on hardware events.
> System generation changes can also be driven by userspace software
> through a dedicated driver ioctl.
>
> Userspace applications or libraries can then (a)synchronously consume
> the system generation counter through the provided FS interface to make
> any necessary internal adjustments following a system generation
> update.
>
> Signed-off-by: Adrian Catangiu <acatan@...zon.com>
> ---
> Documentation/misc-devices/sysgenid.rst | 236 ++++++++++++++++
> Documentation/userspace-api/ioctl/ioctl-number.rst | 1 +
> MAINTAINERS | 8 +
> drivers/misc/Kconfig | 16 ++
> drivers/misc/Makefile | 1 +
> drivers/misc/sysgenid.c | 307 +++++++++++++++++++++
> include/uapi/linux/sysgenid.h | 17 ++
> 7 files changed, 586 insertions(+)
> create mode 100644 Documentation/misc-devices/sysgenid.rst
> create mode 100644 drivers/misc/sysgenid.c
> create mode 100644 include/uapi/linux/sysgenid.h
>
> diff --git a/Documentation/misc-devices/sysgenid.rst b/Documentation/misc-devices/sysgenid.rst
> new file mode 100644
> index 0000000..4337ca0
> --- /dev/null
> +++ b/Documentation/misc-devices/sysgenid.rst
> @@ -0,0 +1,236 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +========
> +SYSGENID
> +========
> +
> +The System Generation ID feature is required in virtualized or
> +containerized environments by applications that work with local copies
> +or caches of world-unique data such as random values, UUIDs,
> +monotonically increasing counters, etc.
> +Such applications can be negatively affected by VM or container
> +snapshotting when the VM or container is either cloned or returned to
> +an earlier point in time.
> +
> +The System Generation ID is a simple concept meant to alleviate the
> +issue by providing a monotonically increasing counter that changes
> +each time the VM or container is restored from a snapshot.
> +The driver for it lives at ``drivers/misc/sysgenid.c``.
> +
> +The ``sysgenid`` driver exposes a monotonic incremental System
> +Generation u32 counter via a char-dev FS interface accessible through
> +``/dev/sysgenid`` that provides sync and async SysGen counter update
> +notifications. It also provides SysGen counter retrieval and
> +confirmation mechanisms.
> +
> +The counter starts from zero when the driver is initialized and
> +monotonically increments every time the system generation changes.
> +
> +The ``sysgenid`` driver exports the ``void sysgenid_bump_generation()``
> +symbol which can be used by backend drivers to drive system generation
> +changes based on hardware events.
> +System generation changes can also be driven by userspace software
> +through a dedicated driver ioctl.
> +
> +Userspace applications or libraries can (a)synchronously consume the
> +system generation counter through the provided FS interface, to make
> +any necessary internal adjustments following a system generation update.
> +
> +Driver FS interface:
> +
> +``open()``:
> + When the device is opened, a copy of the current Sys-Gen-Id (counter)
> + is associated with the open file descriptor. The driver now tracks
> + this file as an independent *watcher*. The driver tracks how many
> + watchers are aware of the latest Sys-Gen-Id counter and how many of
> + them are *outdated*; outdated being those that have lived through
> + a Sys-Gen-Id change but not yet confirmed the new generation counter.
> +
> +``read()``:
> + Read is meant to provide the *new* system generation counter when a
> + generation change takes place. The read operation blocks until the
> + associated counter is no longer up to date, at which point the new
> + counter is provided/returned.
> + Nonblocking ``read()`` uses ``EAGAIN`` to signal that there is no
> + *new* counter value available. The generation counter is considered
> + *new* for each open file descriptor that hasn't confirmed the new
> + value following a generation change. Therefore, once a generation
> + change takes place, all ``read()`` calls will immediately return the
> + new generation counter and will continue to do so until the
> + new value is confirmed back to the driver through ``write()``.
> + Partial reads are not allowed - read buffer needs to be at least
> + 32 bits in size.
> +
> +``write()``:
> + Write is used to confirm the up-to-date Sys Gen counter back to the
> + driver.
> + Following a VM generation change, all existing watchers are marked
> + as *outdated*. Each file descriptor will maintain the *outdated*
> + status until a ``write()`` confirms the up-to-date counter back to
> + the driver.
> + Partial writes are not allowed - write buffer should be exactly
> + 32 bits in size.
> +
> +``poll()``:
> + Poll is implemented to allow polling for generation counter updates.
> + Such updates result in ``EPOLLIN`` polling status until the new
> + up-to-date counter is confirmed back to the driver through a
> + ``write()``.
> +
> +``ioctl()``:
> + The driver also adds support for waiting on open file descriptors
> + that haven't acknowledged a generation counter update, as well as a
> + mechanism for userspace to *force* a generation update:
> +
> + - SYSGENID_WAIT_WATCHERS: blocks until there are no more *outdated*
> + watchers, or if a ``timeout`` argument is provided, until the
> + timeout expires.
> + If the current caller is *outdated* or a generation change happens
> + while waiting (thus making current caller *outdated*), the ioctl
> + returns ``-EINTR`` to signal the user to handle event and retry.
> + - SYSGENID_FORCE_GEN_UPDATE: forces a generation counter increment.
> + It takes a ``minimum-generation`` argument which represents the
> + minimum value the generation counter will be incremented to. For
> + example if current generation is ``5`` and ``SYSGENID_FORCE_GEN_UPDATE(8)``
> + is called, the generation counter will increment to ``8``.
> + This IOCTL can only be used by processes with CAP_CHECKPOINT_RESTORE
> + or CAP_SYS_ADMIN capabilities.
> +
> +``mmap()``:
> + The driver supports ``PROT_READ, MAP_SHARED`` mmaps of a single page
> + in size. The first 4 bytes of the mapped page will contain an
> + up-to-date u32 copy of the system generation counter.
> + The mapped memory can be used as a low-latency generation counter
> + probe mechanism in critical sections - see examples.
>
>From what I have seen this mmap interface is still fundamentally racy.
How about splitting it to a separate patch?
> +``close()``:
> + Removes the file descriptor as a system generation counter *watcher*.
> +
> +Example application workflows
> +-----------------------------
> +
> +1) Watchdog thread simplified example::
> +
> + void watchdog_thread_handler(int *thread_active)
> + {
> + unsigned int genid;
> + int fd = open("/dev/sysgenid", O_RDWR | O_CLOEXEC, S_IRUSR | S_IWUSR);
> +
> + do {
> + // read new gen ID - blocks until VM generation changes
> + read(fd, &genid, sizeof(genid));
> +
> + // because of VM generation change, we need to rebuild world
> + reseed_app_env();
> +
> + // confirm we're done handling gen ID update
> + write(fd, &genid, sizeof(genid));
> + } while (atomic_read(thread_active));
> +
> + close(fd);
> + }
> +
> +2) ASYNC simplified example::
> +
> + void handle_io_on_sysgenfd(int sysgenfd)
> + {
> + unsigned int genid;
> +
> + // read new gen ID - we need it to confirm we've handled update
> + read(fd, &genid, sizeof(genid));
> +
> + // because of VM generation change, we need to rebuild world
> + reseed_app_env();
> +
> + // confirm we're done handling the gen ID update
> + write(fd, &genid, sizeof(genid));
> + }
> +
> + int main() {
> + int epfd, sysgenfd;
> + struct epoll_event ev;
> +
> + epfd = epoll_create(EPOLL_QUEUE_LEN);
> +
> + sysgenfd = open("/dev/sysgenid",
> + O_RDWR | O_CLOEXEC | O_NONBLOCK,
> + S_IRUSR | S_IWUSR);
> +
> + // register sysgenid for polling
> + ev.events = EPOLLIN;
> + ev.data.fd = sysgenfd;
> + epoll_ctl(epfd, EPOLL_CTL_ADD, sysgenfd, &ev);
> +
> + // register other parts of your app for polling
> + // ...
> +
> + while (1) {
> + // wait for something to do...
> + int nfds = epoll_wait(epfd, events,
> + MAX_EPOLL_EVENTS_PER_RUN,
> + EPOLL_RUN_TIMEOUT);
> + if (nfds < 0) die("Error in epoll_wait!");
> +
> + // for each ready fd
> + for(int i = 0; i < nfds; i++) {
> + int fd = events[i].data.fd;
> +
> + if (fd == sysgenfd)
> + handle_io_on_sysgenfd(sysgenfd);
> + else
> + handle_some_other_part_of_the_app(fd);
> + }
> + }
> +
> + return 0;
> + }
> +
> +3) Mapped memory polling simplified example::
> +
> + /*
> + * app/library function that provides cached secrets
> + */
> + char * safe_cached_secret(app_data_t *app)
> + {
> + char *secret;
> + volatile unsigned int *const genid_ptr = get_sysgenid_mapping(app);
> + again:
> + secret = __cached_secret(app);
> +
> + if (unlikely(*genid_ptr != app->cached_genid)) {
> + app->cached_genid = *genid_ptr;
And this is racy, isn't it? There is not system call to synchronize
with interrupts, so the value this reads could be out of date.
> + barrier();
> +
> + // rebuild world then confirm the genid update (thru write)
> + rebuild_caches(app);
> +
> + ack_sysgenid_update(app);
> +
> + goto again;
> + }
> +
> + return secret;
> + }
> +
> +4) Orchestrator simplified example::
> +
> + /*
> + * orchestrator - manages multiple applications and libraries used by
> + * a service and tries to make sure all sensitive components gracefully
> + * handle VM generation changes.
> + * Following function is called on detection of a VM generation change.
> + */
> + int handle_sysgen_update(int sysgen_fd, unsigned int new_gen_id)
> + {
> + // pause until all components have handled event
> + pause_service();
> +
> + // confirm *this* watcher as up-to-date
> + write(sysgen_fd, &new_gen_id, sizeof(unsigned int));
> +
> + // wait for all *others* for at most 5 seconds.
> + ioctl(sysgen_fd, VMGENID_WAIT_WATCHERS, 5000);
> +
> + // all applications on the system have rebuilt worlds
> + resume_service();
> + }
> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
> index a4c75a2..d74fed4 100644
> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> @@ -356,6 +356,7 @@ Code Seq# Include File Comments
> 0xDB 00-0F drivers/char/mwave/mwavepub.h
> 0xDD 00-3F ZFCP device driver see drivers/s390/scsi/
> <mailto:aherrman@...ibm.com>
> +0xE4 01-02 uapi/linux/sysgenid.h SysGenID misc driver
> 0xE5 00-3F linux/fuse.h
> 0xEC 00-01 drivers/platform/chrome/cros_ec_dev.h ChromeOS EC driver
> 0xF3 00-3F drivers/usb/misc/sisusbvga/sisusb.h sisfb (in development)
> diff --git a/MAINTAINERS b/MAINTAINERS
> index d3e847f..f1158b0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17203,6 +17203,14 @@ L: linux-mmc@...r.kernel.org
> S: Maintained
> F: drivers/mmc/host/sdhci-pci-dwc-mshc.c
>
> +SYSGENID
> +M: Adrian Catangiu <acatan@...zon.com>
> +L: linux-kernel@...r.kernel.org
> +S: Supported
> +F: Documentation/misc-devices/sysgenid.rst
> +F: drivers/misc/sysgenid.c
> +F: include/uapi/linux/sysgenid.h
> +
> SYSTEM CONFIGURATION (SYSCON)
> M: Lee Jones <lee.jones@...aro.org>
> M: Arnd Bergmann <arnd@...db.de>
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index fafa8b0..931d716 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -456,6 +456,22 @@ config PVPANIC
> a paravirtualized device provided by QEMU; it lets a virtual machine
> (guest) communicate panic events to the host.
>
> +config SYSGENID
> + tristate "System Generation ID driver"
> + default N
> + help
> + This is a System Generation ID driver which provides a system
> + generation counter. The driver exposes FS ops on /dev/sysgenid
> + through which it can provide information and notifications on system
> + generation changes that happen because of VM or container snapshots
> + or cloning.
> + This enables applications and libraries that store or cache
> + sensitive information, to know that they need to regenerate it
> + after process memory has been exposed to potential copying.
> +
> + To compile this driver as a module, choose M here: the
> + module will be called sysgenid.
> +
> config HISI_HIKEY_USB
> tristate "USB GPIO Hub on HiSilicon Hikey 960/970 Platform"
> depends on (OF && GPIOLIB) || COMPILE_TEST
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index d23231e..4b4933d 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -57,3 +57,4 @@ obj-$(CONFIG_HABANA_AI) += habanalabs/
> obj-$(CONFIG_UACCE) += uacce/
> obj-$(CONFIG_XILINX_SDFEC) += xilinx_sdfec.o
> obj-$(CONFIG_HISI_HIKEY_USB) += hisi_hikey_usb.o
> +obj-$(CONFIG_SYSGENID) += sysgenid.o
> diff --git a/drivers/misc/sysgenid.c b/drivers/misc/sysgenid.c
> new file mode 100644
> index 0000000..95b3421
> --- /dev/null
> +++ b/drivers/misc/sysgenid.c
> @@ -0,0 +1,307 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * System Generation ID driver
> + *
> + * Copyright (C) 2020 Amazon. All rights reserved.
> + *
> + * Authors:
> + * Adrian Catangiu <acatan@...zon.com>
> + *
> + */
> +#include <linux/acpi.h>
> +#include <linux/kernel.h>
> +#include <linux/minmax.h>
> +#include <linux/miscdevice.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/poll.h>
> +#include <linux/random.h>
> +#include <linux/uuid.h>
> +#include <linux/sysgenid.h>
> +
> +struct sysgenid_data {
> + unsigned long map_buf;
> + wait_queue_head_t read_waitq;
> + atomic_t generation_counter;
> +
> + unsigned int watchers;
> + atomic_t outdated_watchers;
> + wait_queue_head_t outdated_waitq;
> + spinlock_t lock;
> +};
> +static struct sysgenid_data sysgenid_data;
> +
> +struct file_data {
> + unsigned int acked_gen_counter;
> +};
> +
> +static void sysgenid_uevent(unsigned int gen_counter);
> +
> +static int equals_gen_counter(unsigned int counter)
> +{
> + return counter == atomic_read(&sysgenid_data.generation_counter);
> +}
> +
> +static void _bump_generation(int min_gen)
> +{
> + unsigned long flags;
> + int counter;
> +
> + spin_lock_irqsave(&sysgenid_data.lock, flags);
> + counter = max(min_gen, 1 + atomic_read(&sysgenid_data.generation_counter));
> + atomic_set(&sysgenid_data.generation_counter, counter);
> + *((int *) sysgenid_data.map_buf) = counter;
> + atomic_set(&sysgenid_data.outdated_watchers, sysgenid_data.watchers);
> +
> + wake_up_interruptible(&sysgenid_data.read_waitq);
> + wake_up_interruptible(&sysgenid_data.outdated_waitq);
> + spin_unlock_irqrestore(&sysgenid_data.lock, flags);
> +
> + sysgenid_uevent(counter);
> +}
> +
> +void sysgenid_bump_generation(void)
> +{
> + _bump_generation(0);
> +}
> +EXPORT_SYMBOL(sysgenid_bump_generation);
> +
> +static void put_outdated_watchers(void)
> +{
> + if (atomic_dec_and_test(&sysgenid_data.outdated_watchers))
> + wake_up_interruptible(&sysgenid_data.outdated_waitq);
> +}
> +
> +static int sysgenid_open(struct inode *inode, struct file *file)
> +{
> + struct file_data *fdata = kzalloc(sizeof(struct file_data), GFP_KERNEL);
> + unsigned long flags;
> +
> + if (!fdata)
> + return -ENOMEM;
> +
> + spin_lock_irqsave(&sysgenid_data.lock, flags);
> + fdata->acked_gen_counter = atomic_read(&sysgenid_data.generation_counter);
> + ++sysgenid_data.watchers;
> + spin_unlock_irqrestore(&sysgenid_data.lock, flags);
> +
> + file->private_data = fdata;
> +
> + return 0;
> +}
> +
> +static int sysgenid_close(struct inode *inode, struct file *file)
> +{
> + struct file_data *fdata = file->private_data;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&sysgenid_data.lock, flags);
> + if (!equals_gen_counter(fdata->acked_gen_counter))
> + put_outdated_watchers();
> + --sysgenid_data.watchers;
> + spin_unlock_irqrestore(&sysgenid_data.lock, flags);
> +
> + kfree(fdata);
> +
> + return 0;
> +}
> +
> +static ssize_t sysgenid_read(struct file *file, char __user *ubuf,
> + size_t nbytes, loff_t *ppos)
> +{
> + struct file_data *fdata = file->private_data;
> + ssize_t ret;
> + int gen_counter;
> +
> + if (nbytes == 0)
> + return 0;
> + /* disallow partial reads */
> + if (nbytes < sizeof(gen_counter))
> + return -EINVAL;
> +
> + if (equals_gen_counter(fdata->acked_gen_counter)) {
> + if (file->f_flags & O_NONBLOCK)
> + return -EAGAIN;
> + ret = wait_event_interruptible(
> + sysgenid_data.read_waitq,
> + !equals_gen_counter(fdata->acked_gen_counter)
> + );
> + if (ret)
> + return ret;
> + }
> +
> + gen_counter = atomic_read(&sysgenid_data.generation_counter);
> + ret = copy_to_user(ubuf, &gen_counter, sizeof(gen_counter));
> + if (ret)
> + return -EFAULT;
> +
> + return sizeof(gen_counter);
interrupt could be in flight at this point. I think you need
to synch with that IRQ otherwise your read will return stale data.
> +}
> +
> +static ssize_t sysgenid_write(struct file *file, const char __user *ubuf,
> + size_t count, loff_t *ppos)
> +{
> + struct file_data *fdata = file->private_data;
> + unsigned int new_acked_gen;
> + unsigned long flags;
> +
> + /* disallow partial writes */
> + if (count != sizeof(new_acked_gen))
> + return -EINVAL;
> + if (copy_from_user(&new_acked_gen, ubuf, count))
> + return -EFAULT;
> +
> + spin_lock_irqsave(&sysgenid_data.lock, flags);
> + /* wrong gen-counter acknowledged */
> + if (!equals_gen_counter(new_acked_gen)) {
> + spin_unlock_irqrestore(&sysgenid_data.lock, flags);
> + return -EINVAL;
> + }
> + if (!equals_gen_counter(fdata->acked_gen_counter)) {
> + fdata->acked_gen_counter = new_acked_gen;
> + put_outdated_watchers();
> + }
> + spin_unlock_irqrestore(&sysgenid_data.lock, flags);
> +
> + return (ssize_t)count;
> +}
> +
> +static __poll_t sysgenid_poll(struct file *file, poll_table *wait)
> +{
> + __poll_t mask = 0;
> + struct file_data *fdata = file->private_data;
> +
> + if (!equals_gen_counter(fdata->acked_gen_counter))
> + return EPOLLIN | EPOLLRDNORM;
> +
> + poll_wait(file, &sysgenid_data.read_waitq, wait);
> +
> + if (!equals_gen_counter(fdata->acked_gen_counter))
> + mask = EPOLLIN | EPOLLRDNORM;
> +
> + return mask;
> +}
> +
> +static long sysgenid_ioctl(struct file *file,
> + unsigned int cmd, unsigned long arg)
> +{
> + struct file_data *fdata = file->private_data;
> + unsigned long timeout_ns, min_gen;
> + ktime_t until;
> + int ret = 0;
> +
> + switch (cmd) {
> + case SYSGENID_WAIT_WATCHERS:
> + timeout_ns = arg * NSEC_PER_MSEC;
> + until = timeout_ns ? ktime_set(0, timeout_ns) : KTIME_MAX;
> +
> + ret = wait_event_interruptible_hrtimeout(
> + sysgenid_data.outdated_waitq,
> + (!atomic_read(&sysgenid_data.outdated_watchers) ||
> + !equals_gen_counter(fdata->acked_gen_counter)),
> + until
> + );
> + break;
> + case SYSGENID_FORCE_GEN_UPDATE:
> + if (!checkpoint_restore_ns_capable(current_user_ns()))
> + return -EACCES;
> + min_gen = arg;
> + _bump_generation(min_gen);
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> + return ret;
> +}
> +
> +static int sysgenid_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct file_data *fdata = file->private_data;
> +
> + if (vma->vm_pgoff != 0 || vma_pages(vma) > 1)
> + return -EINVAL;
> +
> + if ((vma->vm_flags & VM_WRITE) != 0)
> + return -EPERM;
> +
> + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
> + vma->vm_flags &= ~VM_MAYWRITE;
> + vma->vm_private_data = fdata;
> +
> + return vm_insert_page(vma, vma->vm_start,
> + virt_to_page(sysgenid_data.map_buf));
> +}
> +
> +static const struct file_operations fops = {
> + .owner = THIS_MODULE,
> + .mmap = sysgenid_mmap,
> + .open = sysgenid_open,
> + .release = sysgenid_close,
> + .read = sysgenid_read,
> + .write = sysgenid_write,
> + .poll = sysgenid_poll,
> + .unlocked_ioctl = sysgenid_ioctl,
> +};
> +
> +static struct miscdevice sysgenid_misc = {
> + .minor = MISC_DYNAMIC_MINOR,
> + .name = "sysgenid",
> + .fops = &fops,
> +};
> +
> +static void sysgenid_uevent(unsigned int gen_counter)
> +{
> + char event_string[22];
> + char *envp[] = { event_string, NULL };
> + struct device *dev = sysgenid_misc.this_device;
> +
> + if (dev) {
> + sprintf(event_string, "SYSGENID=%u", gen_counter);
> + kobject_uevent_env(&dev->kobj, KOBJ_CHANGE, envp);
> + }
> +}
> +
> +static int __init sysgenid_init(void)
> +{
> + int ret;
> +
> + sysgenid_data.map_buf = get_zeroed_page(GFP_KERNEL);
> + if (!sysgenid_data.map_buf)
> + return -ENOMEM;
> +
> + atomic_set(&sysgenid_data.generation_counter, 0);
> + atomic_set(&sysgenid_data.outdated_watchers, 0);
> + init_waitqueue_head(&sysgenid_data.read_waitq);
> + init_waitqueue_head(&sysgenid_data.outdated_waitq);
> + spin_lock_init(&sysgenid_data.lock);
> +
> + ret = misc_register(&sysgenid_misc);
> + if (ret < 0) {
> + pr_err("misc_register() failed for sysgenid\n");
> + goto err;
> + }
> +
> + return 0;
> +
> +err:
> + free_pages(sysgenid_data.map_buf, 0);
> + sysgenid_data.map_buf = 0;
> +
> + return ret;
> +}
> +
> +static void __exit sysgenid_exit(void)
> +{
> + misc_deregister(&sysgenid_misc);
> + free_pages(sysgenid_data.map_buf, 0);
> + sysgenid_data.map_buf = 0;
> +}
> +
> +module_init(sysgenid_init);
> +module_exit(sysgenid_exit);
> +
> +MODULE_AUTHOR("Adrian Catangiu");
> +MODULE_DESCRIPTION("System Generation ID");
> +MODULE_LICENSE("GPL");
> +MODULE_VERSION("0.1");
> diff --git a/include/uapi/linux/sysgenid.h b/include/uapi/linux/sysgenid.h
> new file mode 100644
> index 0000000..ba370c8
> --- /dev/null
> +++ b/include/uapi/linux/sysgenid.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> +
> +#ifndef _UAPI_LINUX_SYSGENID_H
> +#define _UAPI_LINUX_SYSGENID_H
> +
> +#include <linux/ioctl.h>
> +
> +#define SYSGENID_IOCTL 0xE4
> +#define SYSGENID_WAIT_WATCHERS _IO(SYSGENID_IOCTL, 1)
> +#define SYSGENID_FORCE_GEN_UPDATE _IO(SYSGENID_IOCTL, 2)
> +
> +#ifdef __KERNEL__
> +void sysgenid_bump_generation(void);
> +#endif /* __KERNEL__ */
> +
> +#endif /* _UAPI_LINUX_SYSGENID_H */
> +
> --
> 2.7.4
>
>
>
>
> Amazon Development Center (Romania) S.R.L. registered office: 27A Sf. Lazar Street, UBC5, floor 2, Iasi, Iasi County, 700045, Romania. Registered in Romania. Registration number J22/2621/2005.
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