On Tue, Oct 04, 2011 at 05:37:27PM +1100, Peter Jeremy wrote: > On 2011-Oct-03 01:04:05 +0300, Kostik Belousov <kostik...@gmail.com> wrote: > >Our implementation of pipes does not provide useful values for st_dev > >and st_ino when stat(2) is done on an anonymous pipe. It was noted by the > ... > >Patch below implements the requirement, by the cost of the small overhead > >at the pipe creation time, and slightly bigger cost at the destruction. > > Does it need to be so complex? This information isn't needed by the > kernel and, to be "meaningful", all that is required is that the > (st_dev,st_ino) pair is unique within the system. Given this, > wouldn't it be sufficient to fake up a st_dev and then just make > st_ino be a counter that starts from 0 and increments (atomically?) on > every new pipe? No need to retain state or "free" anything when the > pipe is destroyed. (If necessary, pick a new fake st_dev when st_ino > wraps). Yes, you described the problem. The (st_dev, st_ino) pair must be globally unique in system, not only for the pipes, but for whole domain of file descriptors. This is the reason that I allocate a value for pipe st_dev using the same devfs mechanism as it is done for device numbers. Using simple incrementing counter for pipe inodes, together with allocating yet another st_dev gives essentially the same complications wrt KPI, and feels unclean.
> > >--- a/sys/kern/sys_pipe.c > >+++ b/sys/kern/sys_pipe.c > ... > >+static ino_t pipedev_ino; > .. > >+ ub->st_dev = pipedev_ino; > > st_dev is a dev_t and hence pipedev_ino (which seems misnamed to me) > should probably be dev_t rather than ino_t Fixed. Thank you.
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