On Wed, Mar 07, 2018 at 11:08:56AM -0500, Theodore Y. Ts'o wrote: > This is where it's critcal to understand that the "tune2fs -o" changes > the *default* mount options. The key in the comment is the anything > different from the *filesystem* defaults (that is, the defaults of the > particular ext4 file system, as opposed to the global defaults). The > idea is that /proc/mounts, and /etc/mtab shows the options string that > if used in /etc/fstab, or in the mount command line, will replicate > the current mount option state. Furthermore, that /proc/mounts is the > minimal set of mount option strings. > > You may not like the behavior, but it's been this way forever, and the > reasoning behind it is that the low-level file system code doesn't > really know what the actual mount option string that would be in > /etc/fstab or in the /sbin/mount command line. That's because > /sbin/mount command actually parses the mount options, and things like > "ro" is actually translated into bitflag passed to the mount option. > So for example, it's impossible to know whether "rw" was in the > user-specified mount string, since we never see it by the time the > string gets sent to ext4_fill_super (in fact the kernel never sees > it). So when we try to make /proc/mounts a replacement for /etc/mtab > (since some people make /etc/mtab as symlink /proc/mounts), it's > actually impossible. Trying to make it be the minimal set of options > was at least a consitent thing. That is, if you use "tune2fs -o > nodelalloc", it's not necessary to put nodelalloc in /etc/fstab or in > the mount command line. And hence, it should not be in /proc/mounts.
OK, that makes sense. Thanks. I will work on convincing myself this is how it should be. > As far as where ext4_seq_options_show() gets called, it's because we > have a fair amount of macro shortcuts in fs/ext4/sysfs.c (which is > where we put all of the pseudo file system support for ext4, which > means it includes procfs). Search for macros PROC_FILE_SHOW_DEFN and > PROC_FILE_LIST. Oh that's where it is. -- Len Sorensen