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

[Konstantin Komarov]

From: Eric Biggers <ebiggers@xxxxxxxxxx>
Sent: Friday, December 4, 2020 9:42 PM
> To: Konstantin Komarov <almaz.alexandrovich@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx; viro@xxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; pali@xxxxxxxxxx; dsterba@xxxxxxx;
> aaptel@xxxxxxxx; willy@xxxxxxxxxxxxx; rdunlap@xxxxxxxxxxxxx; joe@xxxxxxxxxxx; mark@xxxxxxxxxxxxx; nborisov@xxxxxxxx;
> linux-ntfs-dev@xxxxxxxxxxxxxxxxxxxxx; anton@xxxxxxxxxx; dan.carpenter@xxxxxxxxxx; hch@xxxxxx
> Subject: Re: [PATCH v14 04/10] fs/ntfs3: Add file operations and implementation
> 
> 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

Hi Eric! We plan to swap spinlock to mutex in the next version.

Best regards!