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 <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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19
mkfs/main.c
19
mkfs/main.c
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@ -1161,18 +1161,25 @@ static int zero_output_file(int out_fd, u64 size)
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{
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int loop_num;
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u64 location = 0;
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char buf[4096];
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char buf[SZ_4K];
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int ret = 0, i;
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ssize_t written;
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memset(buf, 0, 4096);
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loop_num = size / 4096;
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memset(buf, 0, SZ_4K);
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/* Only zero out the first 1M */
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loop_num = SZ_1M / SZ_4K;
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for (i = 0; i < loop_num; i++) {
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written = pwrite64(out_fd, buf, 4096, location);
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if (written != 4096)
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written = pwrite64(out_fd, buf, SZ_4K, location);
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if (written != SZ_4K)
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ret = -EIO;
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location += 4096;
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location += SZ_4K;
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}
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/* Then enlarge the file to size */
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written = pwrite64(out_fd, buf, 1, size - 1);
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if (written < 1)
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ret = -EIO;
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return ret;
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}
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