Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCH] sysfs: Optionally count subdirectories to support buggy applications | Date | Wed, 01 Feb 2012 14:44:32 -0800 |
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Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
> On Wed, Feb 01, 2012 at 02:21:59PM -0800, Eric W. Biederman wrote: >> >> lm_sensors and possibly other applications get confused if all sysfs >> directories return nlink == 1. The lm_sensors code that got confused >> was just wrong and a fixed version of lm_sensors should be released >> shortly. >> >> There may be other applications that have problems with sysfs return >> nlink == 1 for directories. To allow people to continue to use old >> versions of userspace with new kernels add to sysfs a compile time >> option to maintain mostly precise directory counts for those people who >> don't mind the cost. >> >> I have moved where we keep nlink in sysfs_dirent as compared to previous >> versions of subdirectory counting to a location that packs better. >> >> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> >> --- >> fs/sysfs/Kconfig | 15 +++++++++++++++ >> fs/sysfs/dir.c | 8 ++++++++ >> fs/sysfs/inode.c | 2 ++ >> fs/sysfs/sysfs.h | 38 ++++++++++++++++++++++++++++++++++++++ >> 4 files changed, 63 insertions(+), 0 deletions(-) >> >> diff --git a/fs/sysfs/Kconfig b/fs/sysfs/Kconfig >> index 8c41fea..9b403e9 100644 >> --- a/fs/sysfs/Kconfig >> +++ b/fs/sysfs/Kconfig >> @@ -21,3 +21,18 @@ config SYSFS >> example, "root=03:01" for /dev/hda1. >> >> Designers of embedded systems may wish to say N here to conserve space. >> + >> +config SYSFS_COUNT_LINKS >> + bool "sysfs count subdirectoires to support buggy applications" >> + default n > > As we don't want to break things, this should be default y, right?
The new behavior is backwards compatible. What the new behavior is not is bug compatible. So nothing *should* break.
Furthermore the breaking we have seen so far is limited to just lm_sensors. That is exactly one program that is not a server failing to start. That seems pretty minor in the worst case.
So I really don't expect anyone who ships 3.4 to enable this option.
I have written the option solely so that in case my assessment turns out to be wrong there is already a tested solution. I have been through the pain of not being able to upgrade/test a new kernel because of a backwards incompatible change and it can be very unpleasant.
> Also, should we list this in the feature_removal list as well so that we > can get rid of it in a year or so?
Good idea. I don't know if anyone actually reads feature removal but it is good to serve notice. I will cook up a patch for that.
Eric
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