The inode now keeps track of the number of readers/writers.
Inode::BytesInChain() is now only used protected by the request lock.
Implemented some missing POSIX demands:
- when the last writer is closed, all waiting read requests are aborted
- pipefs_write() now returns EPIPE and signals the current thread with
SIGPIPE in case there are no readers left
- pipefs_read() will now return 0 in case there are no writers and no
unread buffers left in the pipe.
git-svn-id: file:///srv/svn/repos/haiku/trunk/current@9717 a95241bf-73f2-0310-859d-f6bbb57e9c96