Re: [PATCH v9 1/8] iov_iter: Define flags to qualify page extraction.

John Hubbard <jhubbard@xxxxxxxxxx> · Tue, 24 Jan 2023 11:23:45 -0800

On 1/24/23 09:01, David Howells wrote:
Define flags to qualify page extraction to pass into iov_iter_*_pages*()
rather than passing in FOLL_* flags.

For now only a flag to allow peer-to-peer DMA is supported.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-block@xxxxxxxxxxxxxxx
---

Notes:
     ver #9)
      - Change extract_flags to extraction_flags.

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>

thanks,
--
John Hubbard
NVIDIA

     
     ver #7)
      - Don't use FOLL_* as a parameter, but rather define constants
        specifically to use with iov_iter_*_pages*().
      - Drop the I/O direction constants for now.

  block/bio.c         |  6 +++---
  block/blk-map.c     |  8 ++++----
  include/linux/uio.h |  7 +++++--
  lib/iov_iter.c      | 14 ++++++++------
  4 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index ab59a491a883..683444e6b711 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1249,7 +1249,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  	unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
  	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
  	struct page **pages = (struct page **)bv;
-	unsigned int gup_flags = 0;
+	unsigned int extraction_flags = 0;
  	ssize_t size, left;
  	unsigned len, i = 0;
  	size_t offset, trim;
@@ -1264,7 +1264,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
  
  	if (bio->bi_bdev && blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue))
-		gup_flags |= FOLL_PCI_P2PDMA;
+		extraction_flags |= ITER_ALLOW_P2PDMA;
  
  	/*
  	 * Each segment in the iov is required to be a block size multiple.
@@ -1275,7 +1275,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
  	 */
  	size = iov_iter_get_pages(iter, pages,
  				  UINT_MAX - bio->bi_iter.bi_size,
-				  nr_pages, &offset, gup_flags);
+				  nr_pages, &offset, extraction_flags);
  	if (unlikely(size <= 0))
  		return size ? size : -EFAULT;
  
diff --git a/block/blk-map.c b/block/blk-map.c
index 19940c978c73..7db52ad5b2d0 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -267,7 +267,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
  {
  	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
  	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
-	unsigned int gup_flags = 0;
+	unsigned int extraction_flags = 0;
  	struct bio *bio;
  	int ret;
  	int j;
@@ -280,7 +280,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
  		return -ENOMEM;
  
  	if (blk_queue_pci_p2pdma(rq->q))
-		gup_flags |= FOLL_PCI_P2PDMA;
+		extraction_flags |= ITER_ALLOW_P2PDMA;
  
  	while (iov_iter_count(iter)) {
  		struct page **pages, *stack_pages[UIO_FASTIOV];
@@ -291,10 +291,10 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
  		if (nr_vecs <= ARRAY_SIZE(stack_pages)) {
  			pages = stack_pages;
  			bytes = iov_iter_get_pages(iter, pages, LONG_MAX,
-						   nr_vecs, &offs, gup_flags);
+						   nr_vecs, &offs, extraction_flags);
  		} else {
  			bytes = iov_iter_get_pages_alloc(iter, &pages,
-						LONG_MAX, &offs, gup_flags);
+						LONG_MAX, &offs, extraction_flags);
  		}
  		if (unlikely(bytes <= 0)) {
  			ret = bytes ? bytes : -EFAULT;
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 9f158238edba..58fda77f6847 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -252,12 +252,12 @@ void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray *
  		     loff_t start, size_t count);
  ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,
  		size_t maxsize, unsigned maxpages, size_t *start,
-		unsigned gup_flags);
+		unsigned extraction_flags);
  ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
  			size_t maxsize, unsigned maxpages, size_t *start);
  ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
  		struct page ***pages, size_t maxsize, size_t *start,
-		unsigned gup_flags);
+		unsigned extraction_flags);
  ssize_t iov_iter_get_pages_alloc2(struct iov_iter *i, struct page ***pages,
  			size_t maxsize, size_t *start);
  int iov_iter_npages(const struct iov_iter *i, int maxpages);
@@ -360,4 +360,7 @@ static inline void iov_iter_ubuf(struct iov_iter *i, unsigned int direction,
  	};
  }
  
+/* Flags for iov_iter_get/extract_pages*() */
+#define ITER_ALLOW_P2PDMA	0x01	/* Allow P2PDMA on the extracted pages */
+
  #endif
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index f9a3ff37ecd1..da7db39075c6 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1432,9 +1432,9 @@ static struct page *first_bvec_segment(const struct iov_iter *i,
  static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
  		   struct page ***pages, size_t maxsize,
  		   unsigned int maxpages, size_t *start,
-		   unsigned int gup_flags)
+		   unsigned int extraction_flags)
  {
-	unsigned int n;
+	unsigned int n, gup_flags = 0;
  
  	if (maxsize > i->count)
  		maxsize = i->count;
@@ -1442,6 +1442,8 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
  		return 0;
  	if (maxsize > MAX_RW_COUNT)
  		maxsize = MAX_RW_COUNT;
+	if (extraction_flags & ITER_ALLOW_P2PDMA)
+		gup_flags |= FOLL_PCI_P2PDMA;
  
  	if (likely(user_backed_iter(i))) {
  		unsigned long addr;
@@ -1495,14 +1497,14 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
  
  ssize_t iov_iter_get_pages(struct iov_iter *i,
  		   struct page **pages, size_t maxsize, unsigned maxpages,
-		   size_t *start, unsigned gup_flags)
+		   size_t *start, unsigned extraction_flags)
  {
  	if (!maxpages)
  		return 0;
  	BUG_ON(!pages);
  
  	return __iov_iter_get_pages_alloc(i, &pages, maxsize, maxpages,
-					  start, gup_flags);
+					  start, extraction_flags);
  }
  EXPORT_SYMBOL_GPL(iov_iter_get_pages);
  
@@ -1515,14 +1517,14 @@ EXPORT_SYMBOL(iov_iter_get_pages2);
  
  ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
  		   struct page ***pages, size_t maxsize,
-		   size_t *start, unsigned gup_flags)
+		   size_t *start, unsigned extraction_flags)
  {
  	ssize_t len;
  
  	*pages = NULL;
  
  	len = __iov_iter_get_pages_alloc(i, pages, maxsize, ~0U, start,
-					 gup_flags);
+					 extraction_flags);
  	if (len <= 0) {
  		kvfree(*pages);
  		*pages = NULL;








