RE: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue of sysfs pagebuf

[Song Bao Hua (Barry Song)]

> -----Original Message-----
> From: Dave Hansen [mailto:dave.hansen@xxxxxxxxx]
> Sent: Friday, April 30, 2021 10:39 AM
> To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx>; tiantao (H)
> <tiantao6@xxxxxxxxxxxxx>; corbet@xxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx
> Cc: linux-doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Rafael J.
> Wysocki <rafael@xxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Valentin
> Schneider <valentin.schneider@xxxxxxx>; Dave Hansen
> <dave.hansen@xxxxxxxxxxxxxxx>; Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Subject: Re: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue
> of sysfs pagebuf
> 
> On 4/29/21 3:32 PM, Song Bao Hua (Barry Song) wrote:
> > $ strace numactl --hardware  2>&1 | grep cpu
> > openat(AT_FDCWD, "/sys/devices/system/cpu",
> > O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node0/cpumap", O_RDONLY) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node1/cpumap", O_RDONLY) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node2/cpumap", O_RDONLY) = 3
> > openat(AT_FDCWD, "/sys/devices/system/node/node3/cpumap", O_RDONLY) = 3
> >
> > If we move to binary, it means we have to change those applications.
> 
> I thought Greg was saying to using a sysfs binary attribute using
> something like like sysfs_create_bin_file().  Those don't have the
> PAGE_SIZE limitation.  But, there's also nothing to keep us from spewing
> nice human-readable text via the "binary" file.
> 
> We don't need to change the file format, just the internal kernel API
> that we produce the files with.

Dave, thanks for clarification. Sounds a way to go.

Barry