Re: [PATCH v14 04/10] fs/ntfs3: Add file operations and implementation

[Eric Biggers]

On Fri, Dec 04, 2020 at 06:45:54PM +0300, Konstantin Komarov wrote:
> +/* external compression lzx/xpress */
> +static int decompress_lzx_xpress(struct ntfs_sb_info *sbi, const char *cmpr,
> +				 size_t cmpr_size, void *unc, size_t unc_size,
> +				 u32 frame_size)
> +{
> +	int err;
> +	void *ctx;
> +
> +	if (cmpr_size == unc_size) {
> +		/* frame not compressed */
> +		memcpy(unc, cmpr, unc_size);
> +		return 0;
> +	}
> +
> +	err = 0;
> +	ctx = NULL;
> +	spin_lock(&sbi->compress.lock);
> +	if (frame_size == 0x8000) {
> +		/* LZX: frame compressed */
> +		if (!sbi->compress.lzx) {
> +			/* Lazy initialize lzx decompress context */
> +			spin_unlock(&sbi->compress.lock);
> +			ctx = lzx_allocate_decompressor(0x8000);
> +			if (!ctx)
> +				return -ENOMEM;
> +			if (IS_ERR(ctx)) {
> +				/* should never failed */
> +				err = PTR_ERR(ctx);
> +				goto out;
> +			}
> +
> +			spin_lock(&sbi->compress.lock);
> +			if (!sbi->compress.lzx) {
> +				sbi->compress.lzx = ctx;
> +				ctx = NULL;
> +			}
> +		}
> +
> +		if (lzx_decompress(sbi->compress.lzx, cmpr, cmpr_size, unc,
> +				   unc_size)) {
> +			err = -EINVAL;
> +		}
> +	} else {
> +		/* XPRESS: frame compressed */
> +		if (!sbi->compress.xpress) {
> +			/* Lazy initialize xpress decompress context */
> +			spin_unlock(&sbi->compress.lock);
> +			ctx = xpress_allocate_decompressor();
> +			if (!ctx)
> +				return -ENOMEM;
> +
> +			spin_lock(&sbi->compress.lock);
> +			if (!sbi->compress.xpress) {
> +				sbi->compress.xpress = ctx;
> +				ctx = NULL;
> +			}
> +		}
> +
> +		if (xpress_decompress(sbi->compress.xpress, cmpr, cmpr_size,
> +				      unc, unc_size)) {
> +			err = -EINVAL;
> +		}
> +	}
> +	spin_unlock(&sbi->compress.lock);
> +out:
> +	ntfs_free(ctx);
> +	return err;
> +}

Decompression is a somewhat heavyweight operation.  Not the type of thing that
should be done while holding a spin lock.

- Eric