Messages in this thread | | | Date | Fri, 2 Jul 2021 14:30:34 -0700 | From | Yury Norov <> | Subject | Re: [PATCH v5 1/3] cpumask: introduce cpumap_print_to_buf to support large bitmask and list |
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On Fri, Jul 02, 2021 at 09:25:57PM +1200, Barry Song wrote: > From: Tian Tao <tiantao6@hisilicon.com> > > The existing cpumap_print_to_pagebuf() is used by cpu topology and other > drivers to export hexadecimal bitmask and decimal list to userspace by > sysfs ABI. > > Right now, those drivers are using a normal attribute for this kind of > ABIs. A normal attribute typically has show entry as below: > > static ssize_t example_dev_show(struct device *dev, > struct device_attribute *attr, char *buf) > { > ... > return cpumap_print_to_pagebuf(true, buf, &pmu_mmdc->cpu); > } > show entry of attribute has no offset and count parameters and this > means the file is limited to one page only. > > cpumap_print_to_pagebuf() API works terribly well for this kind of > normal attribute with buf parameter and without offset, count: > > static inline ssize_t > cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask) > { > return bitmap_print_to_pagebuf(list, buf, cpumask_bits(mask), > nr_cpu_ids); > } > > The problem is once we have many cpus, we have a chance to make bitmask > or list more than one page. Especially for list, it could be as complex > as 0,3,5,7,9,...... We have no simple way to know it exact size. > > It turns out bin_attribute is a way to break this limit. bin_attribute > has show entry as below: > static ssize_t > example_bin_attribute_show(struct file *filp, struct kobject *kobj, > struct bin_attribute *attr, char *buf, > loff_t offset, size_t count) > { > ... > } > > With the new offset and count parameters, this makes sysfs ABI be able > to support file size more than one page. For example, offset could be > >= 4096. > > This patch introduces cpumap_print_to_buf() so that those drivers can > move to bin_attribute to support large bitmask and list. In result, > we have to pass the corresponding parameters from bin_attribute to this > new API. > > Signed-off-by: Tian Tao <tiantao6@hisilicon.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > Cc: Randy Dunlap <rdunlap@infradead.org> > Cc: Stefano Brivio <sbrivio@redhat.com> > Cc: Alexander Gordeev <agordeev@linux.ibm.com> > Cc: "Ma, Jianpeng" <jianpeng.ma@intel.com> > Cc: Yury Norov <yury.norov@gmail.com> > Cc: Valentin Schneider <valentin.schneider@arm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Daniel Bristot de Oliveira <bristot@redhat.com> > Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> > --- > include/linux/cpumask.h | 19 +++++++++++++++++++ > lib/cpumask.c | 18 ++++++++++++++++++ > 2 files changed, 37 insertions(+) > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > index bfc4690de4f4..24f410a2e793 100644 > --- a/include/linux/cpumask.h > +++ b/include/linux/cpumask.h > @@ -983,6 +983,25 @@ cpumap_print_to_pagebuf(bool list, char *buf, const struct cpumask *mask) > nr_cpu_ids); > } > > +/** > + * cpumap_print_to_buf - copies the cpumask into the buffer either > + * as comma-separated list of cpus or hex values of cpumask; > + * Typically used by bin_attribute to export cpumask bitmask and > + * list ABI. > + * @list: indicates whether the cpumap must be list > + * true: print in decimal list format > + * fasle: print in hexadecimal bitmask format > + * @mask: the cpumask to copy > + * @buf: the buffer to copy into > + * @off: in the string from which we are copying, We copy to @buf > + * @count: the maximum number of bytes to print > + * > + * Returns the length of how many bytes have been copied. > + */ > +extern ssize_t > +cpumap_print_to_buf(bool list, char *buf, const struct cpumask *mask, > + loff_t off, size_t count); > + > #if NR_CPUS <= BITS_PER_LONG > #define CPU_MASK_ALL \ > (cpumask_t) { { \ > diff --git a/lib/cpumask.c b/lib/cpumask.c > index c3c76b833384..40421a6d31bc 100644 > --- a/lib/cpumask.c > +++ b/lib/cpumask.c > @@ -279,3 +279,21 @@ int cpumask_any_distribute(const struct cpumask *srcp) > return next; > } > EXPORT_SYMBOL(cpumask_any_distribute); > + > +ssize_t cpumap_print_to_buf(bool list, char *buf, const struct cpumask *mask, > + loff_t off, size_t count) > +{ > + const char *fmt = list ? "%*pbl\n" : "%*pb\n"; > + ssize_t size; > + void *data; > + > + data = kasprintf(GFP_KERNEL, fmt, nr_cpu_ids, cpumask_bits(mask)); > + if (!data) > + return -ENOMEM; > + > + size = memory_read_from_buffer(buf, count, &off, data, strlen(data) + 1); > + kfree(data);
Barry,
It looks like my comments for previous iteration were ignored. I don't like the approach where you allocate potentially big amount of kernel memory just to free it almost immediately. Nor in lib/bitmap, neither in lib/cpumask.
For next iterations, please move this function back to lib/bitmap because there's no specific here for cpumasks.
Thaks, Yury
> + return size; > +} > +EXPORT_SYMBOL(cpumap_print_to_buf); > -- > 2.25.1
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