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 <w...@suse.com>
---
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
--
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