On Feb 23 11:56, Corinna Vinschen wrote: > On Feb 22 22:07, Lasse Collin wrote: > > Eric Blake wrote: > > > On 02/20/2015 01:21 PM, Lasse Collin wrote: > > > > The above Cygwin behavior would make it very easy to add a > > > > workaround to xz for the pipe-data-loss problem: simply don't clear > > > > O_NONBLOCK on stdout. However, I wonder if it is a bug in Cygwin > > > > that the changes to file status flags aren't seen via other file > > > > descriptors that refer to the same file description. If it is a > > > > bug, then the workaround idea will cause trouble in the future when > > > > the bug in Cygwin gets fixed. > > > > > > Yeah, the fact that cygwin is buggy with respect to POSIX may break > > > any workaround you add if cygwin is later patched. > > The problem is two-fold. On one hand there's Windows not supporting > some of the POSIX concepts. So we can't rely on the OS to keep track > of some essential information required to emulate POSIXy behaviour. > So that's where Cygwin needs to keep track of the inforamtion. > > On the other hand there's the way Cygwin works. Cygwin is just a DLL. > It can propagate settings only from parent to child process, or it can > keep shared memory around to share information between processes of the > same user. Most info, as the information stored for descriptors, is > only propagated from parent to child. We could switch to sharing via > shared memory, but that opens up a vector for malicious programs. > > The only safe way around that [...etc...]
It just occured to me, another way to keep info around is what Cygwin's advisory locking does: What we could do is to revamp parts of the code to use per-file description objects in a subdirectory in the native NT "BaseNamedObjects" namespace. That's something we could follow up on when the new account handling stuff is stable enough. > > Alternative idea: Would there be a significant downside if Cygwin > > remembered if non-blocking mode was enabled at some point and close() > > would use that flag instead of the current (non)blocking status to > > determine if the background thread hack should be used? > > No, that should be doable with very minor effort. That's still an option, of course. Corinna -- Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat
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