On Fri, Aug 24, 2018 at 10:38 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Fri, Aug 24, 2018 at 8:05 AM, Theodore Y. Ts'o <tytso@xxxxxxx> wrote: >> On Thu, Aug 23, 2018 at 09:51:00PM -0700, Andy Lutomirski wrote: >>> When this was reviewed earlier, a problem was identified. I asked if >>> it had been addressed. I did *not* say that it was mandatory to >>> address it, nor did I say anything about reworking fs drivers. >>> >>> A reasonable answer might have been "avoiding this pitfall in the new >>> API would involve a large amount of reworking of existing filesystem >>> drivers. I think that the new API, as is, has enough benefits that it >>> makes sense to merge it even with this pitfall, and, if needed, we can >>> introduce an improved version down the road." >> >> It's also not clear that an API that you think is "cleaner" would >> actually be more usable. In fact, I believe it's going to be a sh*t >> show for userspace, because it won't be obvious what will work, and >> what will cause an error of the form, "sorry we can't do this cleaner >> thing that some people think is better". Which means a huge amount of >> special casing in the program, or a lot of very surprising failures >> that will then get exposed to the system administrator, many of whom >> haven't really had much of a problem with the existing mount(8) user >> interface. > > In what way is the kernel better suited to read the mind of the poor > sysadmin, than a userspace helper program? I have a concrete example: mount -oloop. You can leave it to mount(8) to automagically find an existing loop device or setup a new one, or you can do the low level thing and set up your own loop device and mount it. Same story as NFS and friends, except it's not the kernel that does the magic "same source -> same sb" policy but the mount(8) utility. Ever notice the difference? See? And yeah, there are races involved, and userspace is perfectly suited to deal with them. Thanks, Miklos
