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Date: Tue, 8 Oct 2013 19:27:15 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Al Viro <viro@...iv.linux.org.uk> Cc: Al Viro <viro@....linux.org.uk>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [RFC][PATCH 10/13] make dump_emit() use vfs_write() instead of banging at ->f_op->write directly On Tue, Oct 8, 2013 at 7:06 PM, Al Viro <viro@...iv.linux.org.uk> wrote: > On Tue, Oct 08, 2013 at 06:38:47PM -0700, Linus Torvalds wrote: >> On Tue, Oct 8, 2013 at 6:18 PM, Al Viro <viro@...iv.linux.org.uk> wrote: >> > >> > Point, but I would argue that we should yell very loud if we get 0 from >> > vfs_write() for non-zero size. I'm not sure if POSIX allows write(2) >> > to return that, but a lot of userland code won't be expecting that and >> > won't be able to cope... >> >> Actually POSIX very much allows zero returns. O_NDELAY is mentioned as >> a possible cause, in addition to zero-sized writes themselves, of >> course. > > Umm... What it says is "If some data can be written without blocking the > thread, write() shall write what it can and return the number of bytes > written. Otherwise, it shall return -1 and set errno to EAGAIN." Look closer. ".. most historical implementations return zero (with the O_NDELAY flag set, which is the historical predecessor of O_NONBLOCK .." >> Also, writing to (but not past) the end of a block device returns 0 >> for "end of device", iirc. > > What do you mean? If the starting position is below the end of device, > we get a non-zero length write, not exceeding the end. If it's at > the end of device, we get -ENOSPC. It's out of scope for POSIX, but > Linux is definitely acting that way... Hmm. I'm pretty sure I've seen zero returns for EOF somewhere.. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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