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    SubjectRe: [PATCH 02/31] ntsync: Introduce NTSYNC_IOC_CREATE_SEM.
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    On Thursday, 15 February 2024 01:28:32 CST Greg Kroah-Hartman wrote:
    > On Wed, Feb 14, 2024 at 05:36:38PM -0600, Elizabeth Figura wrote:
    > > This corresponds to the NT syscall NtCreateSemaphore().
    > >
    > > Semaphores are one of three types of object to be implemented in this driver,
    > > the others being mutexes and events.
    > >
    > > An NT semaphore contains a 32-bit counter, and is signaled and can be acquired
    > > when the counter is nonzero. The counter has a maximum value which is specified
    > > at creation time. The initial value of the semaphore is also specified at
    > > creation time. There are no restrictions on the maximum and initial value.
    > >
    > > Each object is exposed as an file, to which any number of fds may be opened.
    > > When all fds are closed, the object is deleted.
    > >
    > > Signed-off-by: Elizabeth Figura <zfigura@codeweavers.com>
    > > ---
    > > .../userspace-api/ioctl/ioctl-number.rst | 2 +
    > > drivers/misc/ntsync.c | 120 ++++++++++++++++++
    > > include/uapi/linux/ntsync.h | 21 +++
    > > 3 files changed, 143 insertions(+)
    > > create mode 100644 include/uapi/linux/ntsync.h
    > >
    > > diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
    > > index 457e16f06e04..2f5c6994f042 100644
    > > --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
    > > +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
    > > @@ -173,6 +173,8 @@ Code Seq# Include File Comments
    > > 'M' 00-0F drivers/video/fsl-diu-fb.h conflict!
    > > 'N' 00-1F drivers/usb/scanner.h
    > > 'N' 40-7F drivers/block/nvme.c
    > > +'N' 80-8F uapi/linux/ntsync.h NT synchronization primitives
    > > + <mailto:wine-devel@winehq.org>
    > > 'O' 00-06 mtd/ubi-user.h UBI
    > > 'P' all linux/soundcard.h conflict!
    > > 'P' 60-6F sound/sscape_ioctl.h conflict!
    > > diff --git a/drivers/misc/ntsync.c b/drivers/misc/ntsync.c
    > > index e4969ef90722..3ad86d98b82d 100644
    > > --- a/drivers/misc/ntsync.c
    > > +++ b/drivers/misc/ntsync.c
    > > @@ -5,26 +5,146 @@
    > > * Copyright (C) 2024 Elizabeth Figura
    > > */
    > >
    > > +#include <linux/anon_inodes.h>
    > > +#include <linux/file.h>
    > > #include <linux/fs.h>
    > > #include <linux/miscdevice.h>
    > > #include <linux/module.h>
    > > +#include <linux/slab.h>
    > > +#include <uapi/linux/ntsync.h>
    > >
    > > #define NTSYNC_NAME "ntsync"
    > >
    > > +enum ntsync_type {
    > > + NTSYNC_TYPE_SEM,
    > > +};
    > > +
    > > +struct ntsync_obj {
    > > + enum ntsync_type type;
    > > +
    > > + union {
    > > + struct {
    > > + __u32 count;
    > > + __u32 max;
    > > + } sem;
    > > + } u;
    > > +
    > > + struct file *file;
    > > + struct ntsync_device *dev;
    > > +};
    > > +
    > > +struct ntsync_device {
    > > + struct file *file;
    > > +};
    >
    > No reference counting is needed for your ntsync_device? Or are you
    > relying on the reference counting of struct file here?
    >
    > You pass around pointers to this structure, and save it off into other
    > structures, how do you know it is "safe" to do so?

    Yes, this relies on the reference counting of struct file. The sync
    objects (semaphore etc.) grab a reference when they're created, via
    get_file(), and release it when they're destroyed. This reference is
    taken from within ioctls on the ntsync_device, so the file must be
    valid when we grab a reference. Maybe I'm missing something, though?



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