[PATCH v3 2/2] ndctl: make mmap start at the offset

[Dave Jiang]

Instead of mmap at the beginning of the DAX region, map at the offset
that is aligned down. This reduces the mmap size we need to create.

Signed-off-by: Dave Jiang <dave.ji...@intel.com>
---
 daxctl/io.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/daxctl/io.c b/daxctl/io.c
index 6e07b52..551e831 100644
--- a/daxctl/io.c
+++ b/daxctl/io.c
@@ -46,6 +46,7 @@ struct io_dev {
        const char *parm_path;
        char *real_path;
        uint64_t offset;
+       uint64_t offset_diff;
        enum io_direction direction;
        bool is_dax;
        bool is_char;
@@ -84,7 +85,7 @@ static bool is_stdinout(struct io_dev *io_dev)
 static int setup_device(struct io_dev *io_dev, size_t size)
 {
        int flags, rc;
-       uint64_t align;
+       uint64_t align, offset;
 
        if (is_stdinout(io_dev))
                return 0;
@@ -112,8 +113,11 @@ static int setup_device(struct io_dev *io_dev, size_t size)
 
        io_dev->mmap_size = ALIGN(size, align);
        flags = (io_dev->direction == IO_READ) ? PROT_READ : PROT_WRITE;
+       offset = ALIGN_DOWN(io_dev->offset, align);
+       io_dev->offset_diff = io_dev->offset - offset;
+
        io_dev->mmap = mmap(NULL, io_dev->mmap_size, flags,
-                       MAP_SHARED, io_dev->fd, 0);
+                       MAP_SHARED, io_dev->fd, offset);
        if (io_dev->mmap == MAP_FAILED) {
                rc = -errno;
                perror("mmap");
@@ -372,17 +376,17 @@ static int64_t __do_io(struct io_dev *dst_dev, struct 
io_dev *src_dev,
        ssize_t rc, count = 0;
 
        if (zero && dst_dev->is_dax) {
-               dst = (uint8_t *)dst_dev->mmap + dst_dev->offset;
+               dst = (uint8_t *)dst_dev->mmap + dst_dev->offset_diff;
                memset(dst, 0, len);
                pmem_persist(dst, len);
                rc = len;
        } else if (dst_dev->is_dax && src_dev->is_dax) {
-               src = (uint8_t *)src_dev->mmap + src_dev->offset;
-               dst = (uint8_t *)dst_dev->mmap + dst_dev->offset;
+               src = (uint8_t *)src_dev->mmap + src_dev->offset_diff;
+               dst = (uint8_t *)dst_dev->mmap + dst_dev->offset_diff;
                pmem_memcpy_persist(dst, src, len);
                rc = len;
        } else if (src_dev->is_dax) {
-               src = (uint8_t *)src_dev->mmap + src_dev->offset;
+               src = (uint8_t *)src_dev->mmap + src_dev->offset_diff;
                if (dst_dev->offset) {
                        rc = lseek(dst_dev->fd, dst_dev->offset, SEEK_SET);
                        if (rc < 0) {
@@ -407,7 +411,7 @@ static int64_t __do_io(struct io_dev *dst_dev, struct 
io_dev *src_dev,
                        printf("Requested size %lu larger than source.\n",
                                        len);
        } else if (dst_dev->is_dax) {
-               dst = (uint8_t *)dst_dev->mmap + dst_dev->offset;
+               dst = (uint8_t *)dst_dev->mmap + dst_dev->offset_diff;
                if (src_dev->offset) {
                        rc = lseek(src_dev->fd, src_dev->offset, SEEK_SET);
                        if (rc < 0) {

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