From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from prv3-mh.provo.novell.com ([137.65.250.26]:54162 "EHLO prv3-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751763AbdJTB7R (ORCPT ); Thu, 19 Oct 2017 21:59:17 -0400 From: Qu Wenruo To: linux-btrfs@vger.kernel.org Cc: dsterba@suse.cz Subject: [PATCH 3/7] btrfs-progs: mkfs: Only zero out the first 1M for rootdir Date: Fri, 20 Oct 2017 09:59:03 +0800 Message-Id: <20171020015907.25430-4-wqu@suse.com> In-Reply-To: <20171020015907.25430-1-wqu@suse.com> References: <20171020015907.25430-1-wqu@suse.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: It's a waste of IO to fill the whole image before creating btrfs on it, just wiping the first 1M, and then write 1 byte to the last position to create a sparse file. Signed-off-by: Qu Wenruo --- mkfs/main.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/mkfs/main.c b/mkfs/main.c index 1355089505ca..7b78cfe3550e 100644 --- a/mkfs/main.c +++ b/mkfs/main.c @@ -404,18 +404,25 @@ static int zero_output_file(int out_fd, u64 size) { int loop_num; u64 location = 0; - char buf[4096]; + char buf[SZ_4K]; int ret = 0, i; ssize_t written; - memset(buf, 0, 4096); - loop_num = size / 4096; + memset(buf, 0, SZ_4K); + + /* Only zero out the first 1M */ + loop_num = SZ_1M / SZ_4K; for (i = 0; i < loop_num; i++) { - written = pwrite64(out_fd, buf, 4096, location); - if (written != 4096) + written = pwrite64(out_fd, buf, SZ_4K, location); + if (written != SZ_4K) ret = -EIO; - location += 4096; + location += SZ_4K; } + + /* Then enlarge the file to size */ + written = pwrite64(out_fd, buf, 1, size - 1); + if (written < 1) + ret = -EIO; return ret; } -- 2.14.2