linux-kernel - Re: [PATCH 01/22] scatterlist: Introduce sg

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Message-ID: <20170414083518.GA25471@lst.de>
Date:   Fri, 14 Apr 2017 10:35:18 +0200
From:   Christoph Hellwig <hch@....de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Christoph Hellwig <hch@....de>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...nel.dk>,
        Tejun Heo <tj@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Ming Lin <ming.l@....samsung.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, intel-gfx@...ts.freedesktop.org,
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        sparmaintainer@...sys.com, devel@...verdev.osuosl.org,
        target-devel@...r.kernel.org, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, rds-devel@....oracle.com,
        Steve Wise <swise@...ngridcomputing.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH 01/22] scatterlist: Introduce sg_map helper functions

> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 0007b79..b95934b 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -37,6 +37,9 @@
>  
>  #include <uapi/linux/dma-buf.h>
>  
> +/* Prevent the highmem.h macro from aliasing ops->kunmap_atomic */
> +#undef kunmap_atomic
> +
>  static inline int is_dma_buf_file(struct file *);
>  
>  struct dma_buf_list {

I think the right fix here is to rename the operation to unmap_atomic
and send out a little patch for that ASAP.

> + *   Flags can be any of:
> + *	* SG_KMAP	 - Use kmap to create the mapping
> + *	* SG_KMAP_ATOMIC - Use kmap_atomic to map the page atommically.
> + *			   Thus, the rules of that function apply: the cpu
> + *			   may not sleep until it is unmaped.
> + *
> + *   Also, consider carefully whether this function is appropriate. It is
> + *   largely not recommended for new code and if the sgl came from another
> + *   subsystem and you don't know what kind of memory might be in the list
> + *   then you definitely should not call it. Non-mappable memory may be in
> + *   the sgl and thus this function may fail unexpectedly.
> + **/
> +static inline void *sg_map_offset(struct scatterlist *sg, size_t offset,
> +				   int flags)

I'd rather have separate functions for kmap vs kmap_atomic instead of
the flags parameter.  And while you're at it just always pass the 0
offset parameter instead of adding a wrapper..

Otherwise this looks good to me.