From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: [BUG] fallocate behavior when crossing end-of-file Date: Wed, 06 May 2009 11:10:23 -0400 Message-ID: <1241622623.17493.0.camel@localhost.localdomain> References: <4A018A90.7050109@mccme.ru> <4A01A5DF.5050406@gmail.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Raskin Michael , linux-btrfs@vger.kernel.org To: Edward Shishkin Return-path: In-Reply-To: <4A01A5DF.5050406@gmail.com> List-ID: On Wed, 2009-05-06 at 16:59 +0200, Edward Shishkin wrote: > Raskin Michael wrote: > > Hello. > > > > Hello. > > > I found the following bug in BtrFS: > > > > 1. Create and open an empty file > > 2. fallocate (fd, 0, 1) > > > > Desired: something (probably, one block) is allocated/reserved for the > > file. File length is set to 1 byte. > > > > Where is it documented? > > IMHO we should only guarantee that writes > to [0, 1] won't fail because of lack of disk space. > Other things (including file size) are up to implementation. > This one looks like a pretty simple bug in the fallocate call. It is rounding up the size to a block boundary. -chris > > Actual: A block is allocated. File length is set to 1 block (4096 > > bytes). The rest of the file is filled with zeros. > > > > last_byte = min(extent_map_end(em), alloc_end); > > last_byte = (last_byte + mask) & ~mask; > > if (em->block_start == EXTENT_MAP_HOLE) { > > ret = prealloc_file_range(trans, inode, cur_offset, > > last_byte, locked_end + 1, > > alloc_hint, mode); > > > > That part seems strange to me. You make an effort for block size to > > divide last_byte. But last_byte should be > > max(i_size_read(inode), offset+len) > > - without any rounding. > > > > Michael Raskin > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html