12:45 p.m.
Make the implicit lock explicit, and hold it around blk_* operations.
This allows us to relax the thread model for the filter to
NBDKIT_THREAD_MODEL_PARALLEL.
---
filters/cache/blk.h | 7 ++++++
filters/cache/cache.c | 57 +++++++++++++++++++++++++++++++------------
2 files changed, 49 insertions(+), 15 deletions(-)
diff --git a/filters/cache/blk.h b/filters/cache/blk.h
index 24bf6a1..ab9134e 100644
--- a/filters/cache/blk.h
+++ b/filters/cache/blk.h
@@ -40,6 +40,13 @@ extern int blk_init (void);
/* Close the cache, free the bitmap. */
extern void blk_free (void);
+/*----------------------------------------------------------------------
+ * ** NOTE **
+ *
+ * An exclusive lock must be held when you call any function below
+ * this line.
+ */
+
/* Allocate or resize the cache file and bitmap. */
extern int blk_set_size (uint64_t new_size);
diff --git a/filters/cache/cache.c b/filters/cache/cache.c
index 0d006bc..580e4f5 100644
--- a/filters/cache/cache.c
+++ b/filters/cache/cache.c
@@ -46,6 +46,8 @@
#include <sys/ioctl.h>
#include <assert.h>
+#include <pthread.h>
+
#ifdef HAVE_ALLOCA_H
#include <alloca.h>
#endif
@@ -55,8 +57,12 @@
#include "cache.h"
#include "blk.h"
-/* XXX See design comment in filters/cow/cow.c. */
-#define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS
+#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
+
+/* In order to handle parallel requests safely, this lock must be held
+ * when calling any blk_* functions.
+ */
+static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
enum cache_mode cache_mode = CACHE_MODE_WRITEBACK;
bool cache_on_read = false;
@@ -132,6 +138,7 @@ cache_get_size (struct nbdkit_next_ops *next_ops, void *nxdata,
void *handle)
{
int64_t size;
+ int r;
size = next_ops->get_size (nxdata);
if (size == -1)
@@ -139,7 +146,10 @@ cache_get_size (struct nbdkit_next_ops *next_ops, void *nxdata,
nbdkit_debug ("cache: underlying file size: %" PRIi64, size);
- if (blk_set_size (size))
+ pthread_mutex_lock (&lock);
+ r = blk_set_size (size);
+ pthread_mutex_unlock (&lock);
+ if (r == -1)
return -1;
return size;
@@ -179,6 +189,7 @@ cache_pread (struct nbdkit_next_ops *next_ops, void *nxdata,
while (count > 0) {
uint64_t blknum, blkoffs, n;
+ int r;
blknum = offset / BLKSIZE; /* block number */
blkoffs = offset % BLKSIZE; /* offset within the block */
@@ -186,7 +197,10 @@ cache_pread (struct nbdkit_next_ops *next_ops, void *nxdata,
if (n > count)
n = count;
- if (blk_read (next_ops, nxdata, blknum, block, err) == -1) {
+ pthread_mutex_lock (&lock);
+ r = blk_read (next_ops, nxdata, blknum, block, err);
+ pthread_mutex_unlock (&lock);
+ if (r == -1) {
free (block);
return -1;
}
@@ -225,6 +239,7 @@ cache_pwrite (struct nbdkit_next_ops *next_ops, void *nxdata,
}
while (count > 0) {
uint64_t blknum, blkoffs, n;
+ int r;
blknum = offset / BLKSIZE; /* block number */
blkoffs = offset % BLKSIZE; /* offset within the block */
@@ -232,13 +247,17 @@ cache_pwrite (struct nbdkit_next_ops *next_ops, void *nxdata,
if (n > count)
n = count;
- /* Do a read-modify-write operation on the current block. */
- if (blk_read (next_ops, nxdata, blknum, block, err) == -1){
- free (block);
- return -1;
+ /* Do a read-modify-write operation on the current block.
+ * Hold the lock over the whole operation.
+ */
+ pthread_mutex_lock (&lock);
+ r = blk_read (next_ops, nxdata, blknum, block, err);
+ if (r != -1) {
+ memcpy (&block[blkoffs], buf, n);
+ r = blk_write (next_ops, nxdata, blknum, block, flags, err);
}
- memcpy (&block[blkoffs], buf, n);
- if (blk_write (next_ops, nxdata, blknum, block, flags, err) == -1) {
+ pthread_mutex_unlock (&lock);
+ if (r == -1) {
free (block);
return -1;
}
@@ -278,6 +297,7 @@ cache_zero (struct nbdkit_next_ops *next_ops, void *nxdata,
}
while (count > 0) {
uint64_t blknum, blkoffs, n;
+ int r;
blknum = offset / BLKSIZE; /* block number */
blkoffs = offset % BLKSIZE; /* offset within the block */
@@ -285,12 +305,17 @@ cache_zero (struct nbdkit_next_ops *next_ops, void *nxdata,
if (n > count)
n = count;
- if (blk_read (next_ops, nxdata, blknum, block, err) == -1) {
- free (block);
- return -1;
+ /* Do a read-modify-write operation on the current block.
+ * Hold the lock over the whole operation.
+ */
+ pthread_mutex_lock (&lock);
+ r = blk_read (next_ops, nxdata, blknum, block, err);
+ if (r != -1) {
+ memset (&block[blkoffs], 0, n);
+ r = blk_write (next_ops, nxdata, blknum, block, flags, err);
}
- memset (&block[blkoffs], 0, n);
- if (blk_write (next_ops, nxdata, blknum, block, flags, err) == -1) {
+ pthread_mutex_unlock (&lock);
+ if (r == -1) {
free (block);
return -1;
}
@@ -342,7 +367,9 @@ cache_flush (struct nbdkit_next_ops *next_ops, void *nxdata, void
*handle,
* to be sure. Also we still need to issue the flush to the
* underlying storage.
*/
+ pthread_mutex_lock (&lock);
for_each_dirty_block (flush_dirty_block, &data);
+ pthread_mutex_unlock (&lock);
free (data.block);
/* Now issue a flush request to the underlying storage. */
--
2.19.2