From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Blake Subject: Re: Man page doc for SEEK_DATA/SEEK_HOLE Date: Mon, 19 Sep 2011 12:44:07 -0600 Message-ID: <4E778D77.4070207@redhat.com> References: <4E77827C.3030202@redhat.com> <4E7789A1.4080501@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Josef Bacik , linux-man-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Sunil Mushran Return-path: In-Reply-To: <4E7789A1.4080501-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On 09/19/2011 12:27 PM, Sunil Mushran wrote: > On 09/19/2011 10:57 AM, Eric Blake wrote: >> Also, it seems a shame that the kernel can fail with EINVAL instead of >> properly emulating SEEK_HOLE and SEEK_DATA even on file systems with >> no underlying support for reporting holes. >> > > Why do you say that? If I am reading generic_file_llseek_unlocked() > correctly, the default behavior is treat offset < i_size as data. The proposed wording states: > .B EINVAL > .I whence > -is not one of > -.BR SEEK_SET , > -.BR SEEK_CUR , > -.BR SEEK_END ; > -or the resulting file offset would be negative, > +is not valid (this error may be returned if > +.I whence > +is > +.BR SEEK_DATA > +or > +.BR SEEK_HOLE > +and the underlying file system does not support the operation). I guess it should instead read: EINVAL whence is not valid (this error may be returned if whence is SEEK_DATA or SEEK_HOLE but the kernel does not support the operation). Given your argument that new enough kernels understand SEEK_DATA and SEEK_HOLE for all file systems. I agree that EINVAL will occur if you compile against new enough glibc that exposes the constants, but then run against an older kernel that does not yet understand them. But I want the text to be clarified to be bullet-proof that if I am running against kernel 3.1 or newer, the only way I will ever get EINVAL for these two constants is if I do something else invalid, like a negative offset. -- Eric Blake eblake-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org +1-801-349-2682 Libvirt virtualization library http://libvirt.org -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html