On Mon, Sep 01, 2014 at 02:23:46PM -0700, Andy Lutomirski wrote: > To clarify: do you mean that per-superblock options would all be > strings and would all get passed down to the fs? If so, I like it. I > think that whatever corresponds to MNT_READONLY shouldn't be passed > down to the filesystem or necessarily specified when loading the > filesystem at all. But MNT_READONLY is a very different thing than > "ro". So the way I see it, we should be very clear about the distinction between the mount flags (MS_READONLY) and the mountpoint flags (MNT_READONLY). The former are set when the file system is "mounted" via the call to the file system's fill_super function. The latter is set when the file system is attached to the namespace via the creation of a mount point. From the perspective of the user using the mount(8) userspace program, the way I would envision this working is that the mount(8) progam would query the MS_* flags and use them to populate the MNT_* flags for the initial mount of the file system. That way, the user experience gets preserved, but we move all of the parsing to a single place --- in the kernel. This would also fix the bug where rootflags=noatime doesn't work, because today some mount options are parsed in the kernel, and some are parsed in userspace, and it's really, fundamentally, not fair that the user should be forced to understand the difference between the string "acl" and the magic mount flag, MS_READONLY which happens to be set if "ro" is passed to the mount option alongside "acl". For MS_READONLY, there's no problem because we do currently make a hard distinction between MS_READONLY and MNT_READONLY. The two have distinct meanings, and so I think it makes sense that "ro" be passed down to the file system alongside "acl", even if there is a library function which translates "ro" into the standard MS_READONLY flag. What's more difficult is MS_NOATIME, which exists as a superblock flag, but it's not actually checked as a superblock flag, except to decide whether or not to set MNT_NOATIME. What might make sense is to give the kernel responsibility for parsing the mountpoint flags as well, so we pass text strings for corresponding to MNT_NOATIME, etc. to the kernel as well. If the mountpoint flag isn't specified, then the value of superblock flag (i.e., MS_NOATIME) gets used as the default. Cheers, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
