From 6dd8669a1c52cae1d827d934fbe6171f4893f1ba Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Thu, 19 Oct 2017 14:16:17 +0800 Subject: btrfs-progs: mkfs: Only zero out the first 1M for rootdir 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 Signed-off-by: David Sterba --- mkfs/main.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) (limited to 'mkfs') diff --git a/mkfs/main.c b/mkfs/main.c index 90fab59b..d817ad8d 100644 --- a/mkfs/main.c +++ b/mkfs/main.c @@ -1161,18 +1161,25 @@ 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; } -- cgit v1.2.3