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. thanks, greg k-h
