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Date: Mon, 24 Jun 2013 18:08:44 +1000 From: Dave Chinner <david@...morbit.com> To: Theodore Ts'o <tytso@....edu>, Eric Sandeen <esandeen@...hat.com>, Andreas Dilger <adilger@...ger.ca>, Namjae Jeon <linkinjeon@...il.com>, "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>, "a.sangwan@...sung.com" <a.sangwan@...sung.com>, Namjae Jeon <namjae.jeon@...sung.com> Subject: Re: [PATCH 0/3] ext4: introduce two new ioctls On Sun, Jun 23, 2013 at 11:12:35PM -0400, Theodore Ts'o wrote: > On Mon, Jun 24, 2013 at 12:44:59PM +1000, Dave Chinner wrote: > > > > Hence, at minimum, this should be a fallocate() operation, not a ext4 > > specific ioctl as it is relatively trivial to implement on most > > extent based filesystems. > > The fallocate() uses a units of bytes for the offset and length; would > a FALLOC_FL_COLLAPSE_RANGE be guaranteed to work on any arbitrary > offset and length? Or would it only work if the offset and length are > multiples of the file system blocksize? There's nothing stopping us from restricting the offset/len to specific alignments if the operation cannot be done on arbitrary byte ranges. We do that for direct IO, and the sky hasn't fallen yet. > The the EXT4_IOC_TRUNCATE_BLOCK_RANGE interface solves this problem by > using units of file system blocks (i.e., __u32 start_block), but that > raises another issue, which is it forces the user space program to > somehow figure out the file system block size, which seems a bit nasty. Yeah, exactly. We can do that internally very easily, and EINVAL can be returned when the alignment is bad just like we do for direct IO... But, well, I pine for a generic XFS_IOC_DIOINFO interface so the filesystem can tell users about alignment restrictions.... Cheers, Dave. -- Dave Chinner david@...morbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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