Hi On Mon, Mar 2, 2015 at 9:58 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > On Mon, Mar 02, 2015 at 10:57:43AM -0500, Chuck Lever wrote: >> Hi Chris! >> >> Still in the context of deciding what should go in the FAQ, my >> comments are below. >> >> >> On Mar 2, 2015, at 10:19 AM, Chris Perl <cperl@xxxxxxxxxxxxxx> wrote: >> >> >> I’m in favor of staying more hand-wavy. Otherwise you will end up >> >> making promises you don’t intend to keep ;-) >> > >> > FWIW, I'm in favor of at least some specifics. Something stating that >> > the results of reading from a file while another client holds it open >> > for write are undefined (point 3 of what was already proposed). >> >> The language has to be very careful. >> >> Opens for write are used frequently and by themselves do not cause >> any damage. Corruption risk increases when actual writes occur, >> followed by reads of the same file on other clients, without a >> close and re-open. >> >> Also, any published statement about this could lock us into a >> particular behavior. That makes it harder to improve or change >> (say, to address a bug) in the future. >> >> Specifics can be discussed on the mailing list on a case-by-case >> basis. The specifics depend on a bunch of things, for example: >> >> - which clients are in play >> - which NFS version is in use (delegations and open state) >> - whether reading and writing is in the same byte range >> - whether the file size is changing >> - whether O_DIRECT and mapped files are in use > > These are cases we'd only need to go into if we wanted to give > *stronger* gaurantees than "all bets are off when you don't serialize > with write opens", yes? > > And, sure, that would be interesting, but I think Chris is just asking > for a clearer statement of that basic requirement. > > He's far from the first to assume that the results you'd get from > overlapping opens would be out of date but still reasonable in some > sense, and the FAQ could use a stronger statement that that's not the > case. > > --b. Yes, writing something like; tail -f foo doesn't work if readers and writer aren't on the same client IMO it's the most surprising for someone with a posix background on local fs. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
