On Thu, 2021-03-18 at 17:33 +0800, liuqi (BA) wrote:
> On 2021/3/17 22:57, Joe Perches wrote:
> > On Wed, 2021-03-17 at 17:41 +0800, Qi Liu wrote:
> > > Use the generic sysfs_emit_at() function take place of scnprintf()
> > []
> > > diff --git a/drivers/perf/arm-ccn.c b/drivers/perf/arm-ccn.c
> > []
> > > @@ -328,41 +328,37 @@ static ssize_t arm_ccn_pmu_event_show(struct device
> > > *dev,
> > > struct arm_ccn_pmu_event, attr);
> > > ssize_t res;
> > >
> > >
> > >
> > > - res = scnprintf(buf, PAGE_SIZE, "type=0x%x", event->type);
> > > + res = sysfs_emit(buf, "type=0x%x", event->type);
> > > if (event->event)
> > > - res += scnprintf(buf + res, PAGE_SIZE - res, ",event=0x%x",
> > > + res += sysfs_emit_at(buf + res, res, ",event=0x%x",
> > > event->event);
> >
> > sysfs_emit_at should always use buf, not buf + offset.
> > res should be int and is the offset from buf for the output
> >
> > so the form should be similar to
> >
> > int len;
> >
> > len = sysfs_emit(buf, "type=0x%x", event->type);
> > if (event->event) {
> > len += sysfs_emit_at(buf, len, ",event=0x%x", event->event);
> >
> > etc...
> >
> Hi Joe,
>
> I'll fix the use of sysfs_emit_at in next version, thanks.
> But I think it's better to keep the res as ssize_t, as the return value
> of this function is ssize_t.
The 2nd arg of sysfs_emit_at is int.
On 64 bit platforms, ssize_t is 64 bit while int is 32.
If res (or len) is ssize_t, there could be a lot of -Wconversion warnings
like this produced when using make W=
warning: conversion from ‘ssize_t’ {aka ‘long int’} to ‘int’ may change value
[-Wconversion]
262 | len += sysfs_emit_at(buf, len, "\n");
