Date: Tue, 4 Oct 2011 13:20:48 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Peter Jeremy <peterjeremy@acm.org> Cc: standards@freebsd.org, current@freebsd.org Subject: Re: st_dev and st_ino for pipes Message-ID: <20111004102048.GG1511@deviant.kiev.zoral.com.ua> In-Reply-To: <20111004063727.GA25129@server.vk2pj.dyndns.org> References: <20111002220405.GN1511@deviant.kiev.zoral.com.ua> <20111004063727.GA25129@server.vk2pj.dyndns.org>
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--saLunEaUy7BLkUpu Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Oct 04, 2011 at 05:37:27PM +1100, Peter Jeremy wrote: > On 2011-Oct-03 01:04:05 +0300, Kostik Belousov <kostikbel@gmail.com> wrot= e: > >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. >=20 > 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. >=20 > >--- a/sys/kern/sys_pipe.c > >+++ b/sys/kern/sys_pipe.c > ... > >+static ino_t pipedev_ino; > .. > >+ ub->st_dev =3D pipedev_ino; >=20 > 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. --saLunEaUy7BLkUpu Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (FreeBSD) iEYEARECAAYFAk6K3f8ACgkQC3+MBN1Mb4hTXgCfQFZL163Ze6dJs/qUcGZwcs2O vlAAn2KDt4LVMmSCcF9DyGHn5tRekUEe =3C3S -----END PGP SIGNATURE----- --saLunEaUy7BLkUpu--
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