On 2015-12-07 18:06, Eric Sandeen wrote:
Actually, AFAICT, it's been at least 4.5 decades. Last I checked, this dates back to the original UNIX filesystems, which still updated atimes even when mounted RO.On 12/7/15 2:54 PM, Christoph Anton Mitterer wrote:...2) a section that describes "ro" in btrfs-mount(5) which describes that normal "ro" alone may cause changes on the device and which then refers to hard-ro and/or the list of options (currently nologreplay) which are required right now to make it truly ro. I think this is important as an end-user probably expects "ro" to be truly ro,Yeah, I don't know that this is true. It hasn't been true for over a decade (2?), with the most widely-used filesystem in linux history, i.e. ext3. So if btrfs wants to go on this re-education crusade, more power to you, but I don't know that it's really a fight worth fighting. ;)
Despite this, it really isn't a widely known or well documented behavior outside of developers, forensic specialists, and people who have had to deal with the implications it has on data recovery. There really isn't any way that the user would know about it without being explicitly told, and it's something that can have a serious impact on being able to recover a broken filesystem. TBH, I really feel that _every_ filesystem's documentation should have something about how to make it mount truly read-only, even if it's just a reference to how to mark the block device read-only.
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