Date: Mon, 17 Jul 2006 18:25:03 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: John Baldwin <jhb@freebsd.org> Cc: Igor Sysoev <is@rambler-co.ru>, freebsd-current@freebsd.org Subject: Re: 2Gb SYSVSHM limitation Message-ID: <20060717182314.O26409@fledge.watson.org> In-Reply-To: <200607171256.00539.jhb@freebsd.org> References: <20060712125112.W61255@is.park.rambler.ru> <200607171256.00539.jhb@freebsd.org>
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On Mon, 17 Jul 2006, John Baldwin wrote: > On Wednesday 12 July 2006 04:58, Igor Sysoev wrote: > >> the current kernel limit of SysV memory segment is 2G. Today it is too >> small for amd64 machines. >> >> Year ago Christian S.J. Peron had propsed the patch >> http://people.freebsd.org/~csjp/bigsharedmem.1117028863.diff to increase >> the limit: >> http://freebsd.rambler.ru/bsdmail/freebsd-current_2005/msg05627.html >> >> Are objections against this patch ? > > Well, it breaks the ABI of shminfo. :( Changing the ABI of structures shared > with userspace like this requires duplicate syscalls, etc. to not break > existing binaries (such as existing 6.x amd64 binaries). We're well-overdue for an ABI roll on the System V IPC data structures, but when we do this, we need to be careful to: (a) Provide the compat bits properly. (b) Make sure we fix all the things that need fixing. The current ipc perm data structure contains the following fields: struct ipc_perm { unsigned short cuid; /* creator user id */ unsigned short cgid; /* creator group id */ unsigned short uid; /* user id */ unsigned short gid; /* group id */ unsigned short mode; /* r/w permission */ unsigned short seq; /* sequence # (to generate unique ipcid) */ key_t key; /* user specified msg/sem/shm key */ }; While here, we should fix the above uids and gids do be of appropriate data types. McAfee did the first step here by breaking out kernel and user data structures a few years ago as part of the MAC Framework work, but we'll need new bits to do the next part for compat system calls. Robert N M Watson Computer Laboratory University of Cambridge
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