[PATCH 1/2] block: Do not write past block device boundary during a flush

[Andrey Smirnov]

When calling I/O functions of underlying block device driver we always
need to make sure that its size is small enough to not go past
device's boundary. Not only in get_chunk() and block_cache(), but in
writebuffer_flush() as well. Since the same code is used in three
different places, move it into a subroutine and adjust all of the
calls to ->write()/->read() accordingly.

Signed-off-by: Andrey Smirnov <andrew.smir...@gmail.com>
---
 common/block.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/common/block.c b/common/block.c
index 35173c65f..3a031a4fc 100644
--- a/common/block.c
+++ b/common/block.c
@@ -38,6 +38,11 @@ struct chunk {
 
 #define BUFSIZE (PAGE_SIZE * 4)
 
+static int writebuffer_io_len(struct block_device *blk, struct chunk *chunk)
+{
+       return min(blk->rdbufsize, blk->num_blocks - chunk->block_start);
+}
+
 /*
  * Write all dirty chunks back to the device
  */
@@ -51,7 +56,9 @@ static int writebuffer_flush(struct block_device *blk)
 
        list_for_each_entry(chunk, &blk->buffered_blocks, list) {
                if (chunk->dirty) {
-                       ret = blk->ops->write(blk, chunk->data, 
chunk->block_start, blk->rdbufsize);
+                       ret = blk->ops->write(blk, chunk->data,
+                                             chunk->block_start,
+                                             writebuffer_io_len(blk, chunk));
                        if (ret < 0)
                                return ret;
 
@@ -118,10 +125,9 @@ static struct chunk *get_chunk(struct block_device *blk)
                /* use last entry which is the most unused */
                chunk = list_last_entry(&blk->buffered_blocks, struct chunk, 
list);
                if (chunk->dirty) {
-                       size_t num_blocks = min(blk->rdbufsize,
-                                       blk->num_blocks - chunk->block_start);
-                       ret = blk->ops->write(blk, chunk->data, 
chunk->block_start,
-                                             num_blocks);
+                       ret = blk->ops->write(blk, chunk->data,
+                                             chunk->block_start,
+                                             writebuffer_io_len(blk, chunk));
                        if (ret < 0)
                                return ERR_PTR(ret);
 
@@ -145,7 +151,6 @@ static struct chunk *get_chunk(struct block_device *blk)
 static int block_cache(struct block_device *blk, int block)
 {
        struct chunk *chunk;
-       size_t num_blocks;
        int ret;
 
        chunk = get_chunk(blk);
@@ -157,9 +162,8 @@ static int block_cache(struct block_device *blk, int block)
        dev_dbg(blk->dev, "%s: %d to %d\n", __func__, chunk->block_start,
                chunk->num);
 
-       num_blocks = min(blk->rdbufsize, blk->num_blocks - chunk->block_start);
-
-       ret = blk->ops->read(blk, chunk->data, chunk->block_start, num_blocks);
+       ret = blk->ops->read(blk, chunk->data, chunk->block_start,
+                            writebuffer_io_len(blk, chunk));
        if (ret) {
                list_add_tail(&chunk->list, &blk->idle_blocks);
                return ret;
-- 
2.20.1


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