[PATCH 19/20] Add file data and debugfs read/write commands

[Zach Brown]

On Thu, Jun 12, 2025 at 10:11:11PM +0200, Valerie Aurora wrote:
> Implement ngnfs_data_read() and ngnfs_data_write() and corresponding
> debugfs commands. Also copy over const_ilog2() and related functions
> from the kernel.

> +/*
> + * Calculate the index of the block reference for this logical block
> + * within an indirect block at this level (1 = pointers to data blocks).
> + */
> +static u32 calc_ref_ind(u64 dblk, int level)
> +{
> +	u32 ind;
> +	int i;
> +
> +	BUG_ON(level < 1);
> +
> +	for (i = 1; i < level; i++)
> +		dblk >>= NGNFS_DATA_REFS_PER_BLK_SHIFT;
> +
> +	ind = dblk & (NGNFS_DATA_REFS_PER_BLK - 1ULL);

All this can be a lot smaller with "(>> (shift * level)) & mask).  I
tend to still use the SHIFT/SIZE/MASK convention from PAGE_SIZE, ancient
though that is.

> +/*
> + * Calculate the height of the tree (level of the root pointer) needed
> + * to index the logical block dblk in this file.
> + */
> +static u8 height_from_dblk(u64 dblk)
> +{
> +	u8 height = 2;
> +
> +	if (dblk == 0)
> +		return 1;
> +
> +	while (dblk >>= NGNFS_DATA_REFS_PER_BLK_SHIFT)
> +		height++;

Similarly, this can use (ffs() / shift) with a bit of finesse.

- z