From: Russell King <firstname.lastname@example.org> To: Scott Lurndal <email@example.com> Cc: Gerd Hoffmann <firstname.lastname@example.org>, Matthew Wilcox <email@example.com>, firstname.lastname@example.org, email@example.com, Ulrich Drepper <firstname.lastname@example.org> Subject: Re: [PATCH v2] Add preadv and pwritev system calls. Date: Fri, 12 Dec 2008 19:07:28 +0000 [thread overview] Message-ID: <20081212190728.GC5774@flint.arm.linux.org.uk> (raw) In-Reply-To: <20081212182929.GA9631@pendragon.3leafnetworks.com> On Fri, Dec 12, 2008 at 10:29:29AM -0800, Scott Lurndal wrote: > On Fri, Dec 12, 2008 at 05:02:05PM +0100, Gerd Hoffmann wrote: > > Matthew Wilcox wrote: > > > On the other hand, NetBSD have approximately 0% market share. > > > We shouldn't let them lock us into making a bad decision. Is there > > > anyone other than NetBSD who has added these syscalls? > > > > Free- and OpenBSD have it too. For Solaris I've found a feature request > > only. Dunno about MacOS/Darwin. Other un*xes which are important these > > days? > > > > I'd *really* hate it to have the same system call with different > > argument ordering on different systems though. Especially when swapping > > two integer values, so gcc wouldn't error out on wrong usage. > > I would suggest that from the end-users perspective, the user-mode API > should be similar to pread/pwrite, e.g: > > int preadv(fd, iovec, iovec_size, offset) Yes, and that's easy for glibc to achieve. What's hard is that the user <-> kernel API firstly has a limited number of registers available to it for passing arguments without indirection from user space into kernel space. Secondly, the user <-> kernel argument register allocation can vary depending on the ABI version which user space or kernel space is built for. On ARM we have two ABIs, one where 64-bit arguments can be placed in any two consecutive registers, and one where 64-bit arguments must be placed in an even,odd register pair (not an odd,even pair.) That leads to the above being: fd r0 r0 iovec r1 r1 vecsz r2 r2 offset r3,r4 r4,r5 Notice the different register allocation for the 64-bit offset. This problem of register-aligned argument placement is not limited to just ARM, but several other Linux supported architectures. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of:
next prev parent reply other threads:[~2008-12-12 19:13 UTC|newest] Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-12-12 14:00 Gerd Hoffmann 2008-12-12 15:29 ` Matthew Wilcox 2008-12-12 15:48 ` Gerd Hoffmann 2008-12-12 15:51 ` Matthew Wilcox 2008-12-12 16:02 ` Gerd Hoffmann 2008-12-12 17:03 ` Matthew Wilcox 2008-12-12 18:21 ` Alan Cox 2008-12-12 19:02 ` Russell King 2008-12-12 18:29 ` Scott Lurndal 2008-12-12 19:07 ` Russell King [this message] 2008-12-12 19:56 ` Gerd Hoffmann 2008-12-12 19:56 ` Gerd Hoffmann 2008-12-12 20:12 ` Russell King 2008-12-12 20:39 ` Gerd Hoffmann 2008-12-12 20:39 ` Gerd Hoffmann 2008-12-14 18:19 ` Pavel Machek 2008-12-15 16:37 ` Jennifer Pioch 2008-12-15 20:43 ` Gerd Hoffmann 2008-12-16 9:57 ` Arnd Bergmann 2008-12-17 1:45 ` [osol-code] " Dan Mick 2008-12-17 1:45 ` Dan Mick 2008-12-12 19:47 ` Arnd Bergmann 2008-12-12 20:02 ` Gerd Hoffmann 2008-12-14 11:49 ` Heiko Carstens 2008-12-15 4:14 ` Paul Mackerras 2008-12-15 6:20 ` David Miller 2008-12-12 15:40 ` Ralf Baechle 2008-12-12 16:59 ` Russell King 2008-12-13 1:18 ` Michael Kerrisk
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