Re: Symlink not persisted even after fsync

On Mon, Apr 16, 2018 at 7:07 PM, Dave Chinner wrote: > On Sun, Apr 15, 2018 at 07:10:52PM -0500, Vijay Chidambaram wrote: >> Thanks! As I mentioned before, this is useful. I have a follow-up >> question. Consider the following workload: >> >> creat foo >> link (foo, A/bar)

Re: Symlink not persisted even after fsync

On Sun, Apr 15, 2018 at 07:10:52PM -0500, Vijay Chidambaram wrote: > Thanks! As I mentioned before, this is useful. I have a follow-up > question. Consider the following workload: > > creat foo > link (foo, A/bar) > fsync(foo) > crash > > In this case, after the file system recovers, do we

Re: Symlink not persisted even after fsync

On Mon, Apr 16, 2018 at 12:39 AM, Amir Goldstein wrote: > On Mon, Apr 16, 2018 at 3:10 AM, Vijay Chidambaram > wrote: > [...] >> Consider the following workload: >> >> creat foo >> link (foo, A/bar) >> fsync(foo) >> crash >> >> In this case, after

Re: Symlink not persisted even after fsync

On Mon, Apr 16, 2018 at 12:52 AM, Theodore Y. Ts'o wrote: > On Sun, Apr 15, 2018 at 07:10:52PM -0500, Vijay Chidambaram wrote: >> >> I don't think this is what the paper's ext3-fast does. All the paper >> says is if you have a file system where the fsync of a file persisted >> only

Re: Symlink not persisted even after fsync

On Sun, Apr 15, 2018 at 07:10:52PM -0500, Vijay Chidambaram wrote: > > I don't think this is what the paper's ext3-fast does. All the paper > says is if you have a file system where the fsync of a file persisted > only data related to that file, it would increase performance. > ext3-fast is the

Re: Symlink not persisted even after fsync

On Mon, Apr 16, 2018 at 3:10 AM, Vijay Chidambaram wrote: [...] > Consider the following workload: > > creat foo > link (foo, A/bar) > fsync(foo) > crash > > In this case, after the file system recovers, do we expect foo's link > count to be 2 or 1? I would say 2, but

Re: Symlink not persisted even after fsync

Hi Ted, On Sun, Apr 15, 2018 at 9:13 AM, Theodore Y. Ts'o wrote: > On Sat, Apr 14, 2018 at 08:35:45PM -0500, Vijaychidambaram Velayudhan Pillai > wrote: >> I was one of the authors on that paper, and I didn't know until today you >> didn't like that work :) The paper did *not*

Re: Symlink not persisted even after fsync

On Sat, Apr 14, 2018 at 08:35:45PM -0500, Vijaychidambaram Velayudhan Pillai wrote: > I was one of the authors on that paper, and I didn't know until today you > didn't like that work :) The paper did *not* suggest we support invented > guarantees without considering the performance impact. I

Re: Symlink not persisted even after fsync

Hi Ted, On Sat, Apr 14, 2018 at 8:30 PM, Theodore Y. Ts'o wrote: > When you open "foo", the restulting file descriptor is not associated > with the symlink. The resulting file descriptor is the exact same > thing you would get if you had instead called: > > fd =

Re: Symlink not persisted even after fsync

Hi Ted, Thanks for the reply. On Sat, Apr 14, 2018 at 8:17 PM, Theodore Y. Ts'o wrote: > > The only thing I would add to Dave's comments is that a lot of these > formal semantics are de facto, and not de jure. If you take a look at > POSIX or the Single Unix Specification, they

Re: Symlink not persisted even after fsync

On Sat, Apr 14, 2018 at 08:13:28PM -0500, Vijay Chidambaram wrote: > > We are *not* saying an fsync on a symlink file has to result in any > action on the original file. We understand the lack of ordering > constraints here. The problem is you're not being precise here. The fsync(2) system call

Re: Symlink not persisted even after fsync

Hi Dave, Thank you for your detailed reply. I think we still have a misunderstanding. Bear with me, much of this may seem obvious to you, but not to us and future readers of this mailing list :) We are *not* saying an fsync on a symlink file has to result in any action on the original file. We

Re: Symlink not persisted even after fsync

On Fri, Apr 13, 2018 at 10:27:56PM -0500, Vijay Chidambaram wrote: > Hi Dave, > > Thanks for the reply. > > I feel like we are not talking about the same thing here. > > What we are asking is: if you perform > > fsync(symlink) > crash > > can we expect it to see the symlink file in the parent

Re: Symlink not persisted even after fsync

Hi Dave, Thanks for the reply. I feel like we are not talking about the same thing here. What we are asking is: if you perform fsync(symlink) crash can we expect it to see the symlink file in the parent directory after a crash given we didn't fsync the parent directory? Amir argues we can't

Re: Symlink not persisted even after fsync

On Fri, Apr 13, 2018 at 09:39:27AM -0500, Jayashree Mohan wrote: > Hey Dave, > > Thanks for clarifying the crash recovery semantics of strictly > metadata ordered filesystems. We had a follow-up question in this > case. > > On Fri, Apr 13, 2018 at 8:16 AM, Amir Goldstein

Re: Symlink not persisted even after fsync

Hey Dave, Thanks for clarifying the crash recovery semantics of strictly metadata ordered filesystems. We had a follow-up question in this case. On Fri, Apr 13, 2018 at 8:16 AM, Amir Goldstein wrote: > On Fri, Apr 13, 2018 at 3:54 PM, Vijay Chidambaram

Re: Symlink not persisted even after fsync

On Fri, Apr 13, 2018 at 08:52:19AM +0300, Amir Goldstein wrote: > On Thu, Apr 12, 2018 at 8:51 PM, Jayashree Mohan > wrote: > > Hi, > > > > We came across what seems to be a crash consistency bug on btrfs and > > f2fs. When we create a symlink for a file and fsync the

Re: Symlink not persisted even after fsync

On Fri, Apr 13, 2018 at 3:54 PM, Vijay Chidambaram wrote: > Hi Amir, > > Thanks for the reply! > > On Fri, Apr 13, 2018 at 12:52 AM, Amir Goldstein wrote: >> >> Not a bug. >> >> From man 2 fsync: >> >> "Calling fsync() does not necessarily ensure that

Re: Symlink not persisted even after fsync

Hi Amir, Thanks for the reply! On Fri, Apr 13, 2018 at 12:52 AM, Amir Goldstein wrote: > > Not a bug. > > From man 2 fsync: > > "Calling fsync() does not necessarily ensure that the entry in the > directory containing the file has also reached disk. For that an >

Re: Symlink not persisted even after fsync

On Thu, Apr 12, 2018 at 8:51 PM, Jayashree Mohan wrote: > Hi, > > We came across what seems to be a crash consistency bug on btrfs and > f2fs. When we create a symlink for a file and fsync the symlink, on > recovery from crash, the fsync-ed file is missing. > > You can

Symlink not persisted even after fsync

Hi, We came across what seems to be a crash consistency bug on btrfs and f2fs. When we create a symlink for a file and fsync the symlink, on recovery from crash, the fsync-ed file is missing. You can reproduce this behaviour using this minimal workload : 1. symlink (foo, bar) 2. open bar 3.