Re: [PATCH] btrfs-progs: mkfs: use device_discard_blocks() to replace prepare_discard_device()

[Roman Mamedov <rm@romanrm.net>]

On Thu,  8 Jan 2026 15:12:17 +1030
Qu Wenruo <wqu@suse.com> wrote:

> -static void prepare_discard_device(const char *filename, int fd, u64 byte_count, unsigned opflags)
> -{
> -	u64 cur = 0;
> -
> -	while (cur < byte_count) {
> -		/* 1G granularity */
> -		u64 chunk_size = (cur == 0) ? SZ_1M : min_t(u64, byte_count - cur, SZ_1G);
> -		int ret;
> -
> -		ret = discard_range(fd, cur, chunk_size);
> -		if (ret)
> -			return;
> -		/*
> -		 * The first range discarded successfully, meaning the device supports
> -		 * discard.
> -		 */
> -		if (opflags & PREP_DEVICE_VERBOSE && cur == 0)
> -			printf("Performing full device TRIM %s (%s) ...\n",
> -			       filename, pretty_size(byte_count));
> -		cur += chunk_size;
> -	}
> -}
> -
>  /*
>   * Write zeros to the given range [start, start + len)
>   */
> @@ -293,8 +270,16 @@ int btrfs_prepare_device(int fd, const char *file, u64 *byte_count_ret,
>  		goto err;
>  	}
>  
> -	if (!(opflags & PREP_DEVICE_ZONED) && (opflags & PREP_DEVICE_DISCARD))
> -		prepare_discard_device(file, fd, byte_count, opflags);
> +	if (!(opflags & PREP_DEVICE_ZONED) && (opflags & PREP_DEVICE_DISCARD)) {
> +		ret = device_discard_blocks(fd, 0, byte_count);
> +		if (ret < 0) {
> +			errno = -ret;
> +			warning("failed to discard device '%s': %m", file);
> +		} else {
> +			printf("Performing full device TRIM %s (%s) ...\n",
> +			       file, pretty_size(byte_count));
> +		}
> +	}
>  
>  	ret = btrfs_wipe_existing_sb(fd, zinfo);
>  	if (ret < 0) {

Before: the message is printed after the first successful discard of a 1G
range, so with any real-world device at the very beginning of operation.

After: the message is printed only after the full device is discarded???
And it still implies the operation has just begun and is in progress.

It could take a significant time and it was good to print it in the beginning
to let the user know what is going on.

Or I am missing something here?

-- 
With respect,
Roman