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Date: Thu, 16 Dec 2010 21:56:38 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: Richard Cochran <richardcochran@...il.com>
cc: linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
netdev@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
Arnd Bergmann <arnd@...db.de>,
Christoph Lameter <cl@...ux.com>,
David Miller <davem@...emloft.net>,
John Stultz <johnstul@...ibm.com>,
Krzysztof Halasa <khc@...waw.pl>,
Peter Zijlstra <peterz@...radead.org>,
Rodolfo Giometti <giometti@...ux.it>
Subject: Re: [PATCH V7 3/8] posix clocks: introduce dynamic clocks
On Thu, 16 Dec 2010, Richard Cochran wrote:
> --- /dev/null
> +++ b/include/linux/posix-clock.h
> +/**
> + * struct posix_clock_fops - character device operations
> + *
> + * Every posix clock is represented by a character device. Drivers may
> + * optionally offer extended capabilities by implementing these
> + * functions. The character device file operations are first handled
> + * by the clock device layer, then passed on to the driver by calling
> + * these functions.
> + *
> + * The clock device layer already uses fp->private_data, so drivers
> + * are provided their private data via the 'priv' paramenter.
> + */
> +void *posix_clock_private(struct file *fp);
Leftover ? There is neither a caller nor an implementation
> +struct posix_clock_fops {
> + int (*fasync) (void *priv, int fd, struct file *file, int on);
> + int (*mmap) (void *priv, struct vm_area_struct *vma);
> + int (*open) (void *priv, fmode_t f_mode);
> + int (*release) (void *priv);
> + long (*ioctl) (void *priv, unsigned int cmd, unsigned long arg);
> + long (*compat_ioctl) (void *priv, unsigned int cmd, unsigned long arg);
Do we really need a compat_ioctl ?
> + ssize_t (*read) (void *priv, uint flags, char __user *buf, size_t cnt);
> + unsigned int (*poll) (void *priv, struct file *file, poll_table *wait);
> --- a/kernel/time/Makefile
> +++ b/kernel/time/Makefile
> @@ -1,4 +1,5 @@
> -obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o timecompare.o timeconv.o
> +obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o \
> +timecompare.o timeconv.o posix-clock.o
Please start a new obj-y += line instead
> --- /dev/null
> +++ b/kernel/time/posix-clock.c
> +
> +#define MAX_CLKDEV BITS_PER_LONG
Please put some more space between the MAX_CLKDEV and BITS_PER_LONG. I
had to look three times to not read it as a single word.
> +static DECLARE_BITMAP(clocks_map, MAX_CLKDEV);
> +static DEFINE_MUTEX(clocks_mutex); /* protects 'clocks_map' */
Please avoid tail comments
> +struct posix_clock {
> + struct posix_clock_operations *ops;
> + struct cdev cdev;
> + struct kref kref;
> + struct mutex mux;
> + void *priv;
You can get away with that private pointer and all the void *
arguments to the various posix_clock_operations, if you mandate that
the posix_clock_operations are embedded into a clock specific data
structure.
So void *priv would become struct posix_clock_operations *clkops and
you can get your private data in the clock implementation with
container_of().
> + int index;
> + bool zombie;
Ths field is only set, but nowhere else used. What's the purpose ?
Leftover ?
> +};
> +
> +static void delete_clock(struct kref *kref);
> +
> +
> +static int posix_clock_open(struct inode *inode, struct file *fp)
> +{
> + struct posix_clock *clk =
> + container_of(inode->i_cdev, struct posix_clock, cdev);
> +
> + kref_get(&clk->kref);
> + fp->private_data = clk;
fp->private_data should only be set on success. And this will leak a
ref count when the clock open function fails.
What's that kref protecting here ?
> +
> + if (clk->ops->fops.open)
> + return clk->ops->fops.open(clk->priv, fp->f_mode);
> + else
> + return 0;
> +}
> +
> +static int posix_clock_release(struct inode *inode, struct file *fp)
> +{
> + struct posix_clock *clk = fp->private_data;
> + int err = 0;
fp->private_data should be set to NULL in the release function.
> + if (clk->ops->fops.release)
> + err = clk->ops->fops.release(clk->priv);
> +
> + kref_put(&clk->kref, delete_clock);
> +struct posix_clock *posix_clock_create(struct posix_clock_operations *cops,
> + dev_t devid, void *priv)
> +{
> + struct posix_clock *clk;
> + int err;
> +
> + mutex_lock(&clocks_mutex);
> +
> + err = -ENOMEM;
> + clk = kzalloc(sizeof(*clk), GFP_KERNEL);
> + if (!clk)
> + goto no_memory;
> +
> + err = -EBUSY;
> + clk->index = find_first_zero_bit(clocks_map, MAX_CLKDEV);
> + if (clk->index < MAX_CLKDEV)
> + set_bit(clk->index, clocks_map);
> + else
> + goto no_index;
if (clk->index >= MAX_CLKDEV)
goto no_index;
set_bit(clk->index, clocks_map);
Makes it better readable.
> +static void delete_clock(struct kref *kref)
> +{
> + struct posix_clock *clk =
> + container_of(kref, struct posix_clock, kref);
> +
> + mutex_lock(&clocks_mutex);
> + clear_bit(clk->index, clocks_map);
> + mutex_unlock(&clocks_mutex);
> +
> + mutex_destroy(&clk->mux);
> + kfree(clk);
> +}
> +
> +void posix_clock_destroy(struct posix_clock *clk)
> +{
> + cdev_del(&clk->cdev);
> +
> + mutex_lock(&clk->mux);
> + clk->zombie = true;
> + mutex_unlock(&clk->mux);
> +
> + kref_put(&clk->kref, delete_clock);
I still have some headache to understand that kref / delete_clock
magic here.
Thanks,
tglx
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