From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay2.corp.sgi.com [137.38.102.29]) by oss.sgi.com (Postfix) with ESMTP id 7913D7FB2 for ; Wed, 21 Aug 2013 14:58:49 -0500 (CDT) Message-ID: <52151BF8.8070506@sgi.com> Date: Wed, 21 Aug 2013 14:58:48 -0500 From: Mark Tinguely MIME-Version: 1.0 Subject: Re: [PATCH] xfs_io: add the lseek() SEEK_DATA/SEEK_HOLE support References: <20130816205409.976658624@sgi.com> <5213F6AF.8070107@sandeen.net> <5214CB5C.4050608@sgi.com> <5214EAAC.80800@sandeen.net> <5214F050.7060402@sgi.com> <52150775.1050705@sandeen.net> <521512E3.7090301@sgi.com> <5215170F.3050703@sandeen.net> In-Reply-To: <5215170F.3050703@sandeen.net> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: xfs-bounces@oss.sgi.com Sender: xfs-bounces@oss.sgi.com To: Eric Sandeen Cc: xfs@oss.sgi.com On 08/21/13 14:37, Eric Sandeen wrote: > On 8/21/13 2:20 PM, Mark Tinguely wrote: >> On 08/21/13 13:31, Eric Sandeen wrote: > > ... > >>>> There are different versions of XFS seek_data and they will >>>> detect/report the start of data and holes differently so output >>>> parsing will be a bear. The existing C code sends the 2 different >>>> value numbers that could be reported. >>> >>> are they ... both correct? If one is a bug, it can just be a bug, right? >>> I'm sorry I'm not up on the history. >> >> Lets say we have a file >> hole 0-4K >> data 4K-8K >> hole 8-12K >> data 12-16K >> >> for data/hole check starting at offset 0, valid response are >> 0K or 4K for data >> 0K or 16K or -1 for holes >> >> This feature and test was for Jeff fine-tuned seek_data/seek_hole support. The tests would be more specific to that feature and output is specific. > > Well, at least the man page says: > >> SEEK_DATA >> Adjust the file offset to the next location in the file greater than >> or equal to offset containing data. If offset points to data, then >> the file offset is set to offset. > > So above, if we say "SEEK_DATA at offset 0" it seems like 0k is clearly wrong, and 4k is clearly right. If the implementation can't really detect a hole, then everything is data. > >> SEEK_HOLE >> Adjust the file offset to the next hole in the file greater than or >> equal to offset. If offset points into the middle of a hole, then the >> file offset is set to offset. If there is no hole past offset, then >> the file offset is adjusted to the end of the file (i.e., there is an >> implicit hole at the end of any file). > > and "SEEK_HOLE at offset 0" should pretty clearly return 0, and 16k would be wrong. probably my bad notation - the data started at 12K ended at 16K-1. Some report the hole at the end of the file in bytes (16k), some cases as -1. Real fun stuff. The current seek_data/seek_hole xfstest correct for this in the C code by say what values it will accept as being good. > > It's not POSIX yet, so I guess there's no gospel, but that's what the man page says. > > -Eric --Mark. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs