> -----Original Message----- > From: gregkh@xxxxxxxxxxxxxxxxxxx [mailto:gregkh@xxxxxxxxxxxxxxxxxxx] > Sent: Friday, July 23, 2021 11:29 PM > To: Song Bao Hua (Barry Song) <song.bao.hua@xxxxxxxxxxxxx> > Cc: Dave Hansen <dave.hansen@xxxxxxxxx>; tiantao (H) <tiantao6@xxxxxxxxxxxxx>; > corbet@xxxxxxx; 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>; Linuxarm <linuxarm@xxxxxxxxxx> > Subject: Re: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue > of sysfs pagebuf > > On Fri, Jul 23, 2021 at 11:20:19AM +0000, Song Bao Hua (Barry Song) wrote: > > > > > > > -----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. > > > > Sorry for waking-up the old thread. > > > > I am not sure how common a regular device_attribute will be larger than > > 4KB and have to work around by bin_attribute. But I wrote a prototype > > which can initially support large regular sysfs entry and be able to > > fill the entire buffer by only one show() entry. The other words to say, > > we don't need to call read() of bin_attribute multiple times for a large > > regular file. Right now, only read-only attribute is supported. > > > > Subject: [RFC PATCH] sysfs: support regular device attr which can be larger > than > > PAGE_SIZE > > > > A regular sysfs ABI could be more than 4KB, right now, we are using > > bin_attribute to workaround and break this limit. A better solution > > would be supporting long device attribute. In this case, we will > > still be able to enjoy the advantages of buffering and seeking of > > seq file and only need to fill the entire buffer of sysfs entry > > once. > > No, please no. I WANT people to run into this problem and realize that > it went totally wrong because they should not be having more than one > "value" in a sysfs file like this. > > Let's not make it easy on people please, moving to a bin attribute is a > big deal, let's keep it that way. Ok. Got it. Thanks for clarification. That was the experiment I made recently when I almost got totally stuck. > > thanks, > > greg k-h Thanks Barry
