[Libguestfs] [PATCH nbdkit] plugins, filters: Define and use NBDKIT_HANDLE_NOT_NEEDED.
Richard W.M. Jones
rjones at redhat.com
Tue Jan 1 14:31:17 UTC 2019
A common idiom where we don't need a per-connection handle is:
static void *
myplugin_open (int readonly)
{
static int handle;
return &handle;
}
We need to return some non-NULL value, but we don't care what.
This commit defines a macro NBDKIT_HANDLE_NOT_NEEDED which contains a
meaningless non-NULL pointer which can be used instead of the above.
This is more descriptive than the previous code.
---
docs/nbdkit-filter.pod | 3 ++-
docs/nbdkit-plugin.pod | 3 ++-
include/nbdkit-common.h | 5 +++++
filters/cache/cache.c | 7 +------
filters/cow/cow.c | 7 +------
filters/error/error.c | 4 +---
plugins/example1/example1.c | 7 +++----
plugins/floppy/floppy.c | 7 +------
plugins/full/full.c | 4 +---
plugins/iso/iso.c | 7 +------
plugins/memory/memory.c | 5 +----
plugins/null/null.c | 4 +---
plugins/partitioning/partitioning.c | 5 +----
plugins/pattern/pattern.c | 5 +----
plugins/random/random.c | 5 +----
15 files changed, 23 insertions(+), 55 deletions(-)
diff --git a/docs/nbdkit-filter.pod b/docs/nbdkit-filter.pod
index 77ecd7b..dd5c4ed 100644
--- a/docs/nbdkit-filter.pod
+++ b/docs/nbdkit-filter.pod
@@ -281,7 +281,8 @@ to other filter callbacks and could be freed in the C<.close>
callback.
Note that the handle is completely opaque to nbdkit, but it must not
-be NULL.
+be NULL. If you don't need to use a handle, return
+C<NBDKIT_HANDLE_NOT_NEEDED> which is a meaningless non-NULL pointer.
If there is an error, C<.open> should call C<nbdkit_error> with an
error message and return C<NULL>.
diff --git a/docs/nbdkit-plugin.pod b/docs/nbdkit-plugin.pod
index 0f8ef79..e909b0d 100644
--- a/docs/nbdkit-plugin.pod
+++ b/docs/nbdkit-plugin.pod
@@ -453,7 +453,8 @@ is passed back to other callbacks and could be freed in the C<.close>
callback.
Note that the handle is completely opaque to nbdkit, but it must not
-be NULL.
+be NULL. If you don't need to use a handle, return
+C<NBDKIT_HANDLE_NOT_NEEDED> which is a meaningless non-NULL pointer.
The C<readonly> flag informs the plugin that the user requested a
read-only connection using the I<-r> flag on the command line. Note
diff --git a/include/nbdkit-common.h b/include/nbdkit-common.h
index 9295b8a..bc3c438 100644
--- a/include/nbdkit-common.h
+++ b/include/nbdkit-common.h
@@ -70,6 +70,11 @@ extern int nbdkit_parse_bool (const char *str);
extern int nbdkit_read_password (const char *value, char **password);
extern char *nbdkit_realpath (const char *path);
+/* A meaningless non-NULL pointer which can be used when you don't
+ * need a per-connection handle.
+ */
+#define NBDKIT_HANDLE_NOT_NEEDED ((void *) &nbdkit_error)
+
#ifdef __cplusplus
}
#endif
diff --git a/filters/cache/cache.c b/filters/cache/cache.c
index 67dde23..dc7ceab 100644
--- a/filters/cache/cache.c
+++ b/filters/cache/cache.c
@@ -177,15 +177,10 @@ cache_config_complete (nbdkit_next_config_complete *next, void *nxdata)
static void *
cache_open (nbdkit_next_open *next, void *nxdata, int readonly)
{
- /* We don't use the handle, so this just provides a non-NULL
- * pointer that we can return.
- */
- static int handle;
-
if (next (nxdata, readonly) == -1)
return NULL;
- return &handle;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
/* Get the file size and ensure the cache is the correct size. */
diff --git a/filters/cow/cow.c b/filters/cow/cow.c
index fe5b00e..b8f08c4 100644
--- a/filters/cow/cow.c
+++ b/filters/cow/cow.c
@@ -70,16 +70,11 @@ cow_unload (void)
static void *
cow_open (nbdkit_next_open *next, void *nxdata, int readonly)
{
- /* We don't use the handle, so this just provides a non-NULL
- * pointer that we can return.
- */
- static int handle;
-
/* Always pass readonly=1 to the underlying plugin. */
if (next (nxdata, 1) == -1)
return NULL;
- return &handle;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
/* Get the file size and ensure the overlay is the correct size. */
diff --git a/filters/error/error.c b/filters/error/error.c
index c897c76..598bd1f 100644
--- a/filters/error/error.c
+++ b/filters/error/error.c
@@ -240,12 +240,10 @@ error_config (nbdkit_next_config *next, void *nxdata,
static void *
error_open (nbdkit_next_open *next, void *nxdata, int readonly)
{
- static int handle;
-
if (next (nxdata, readonly) == -1)
return NULL;
- return &handle;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
/* This function injects a random error. */
diff --git a/plugins/example1/example1.c b/plugins/example1/example1.c
index 871efb7..ddafc60 100644
--- a/plugins/example1/example1.c
+++ b/plugins/example1/example1.c
@@ -131,11 +131,10 @@ static void *
example1_open (int readonly)
{
/* In this trivial example we don't care about per-connection
- * handles (every connection serves up the same content and there is
- * no connection state), so we just have to return something that is
- * non-NULL and doesn't need to be freed.
+ * handles because every connection serves up the same content and
+ * there is no connection state.
*/
- return data;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
/* Size of the data we are going to serve. */
diff --git a/plugins/floppy/floppy.c b/plugins/floppy/floppy.c
index 769448c..5e23c88 100644
--- a/plugins/floppy/floppy.c
+++ b/plugins/floppy/floppy.c
@@ -110,12 +110,7 @@ floppy_config_complete (void)
static void *
floppy_open (int readonly)
{
- /* We don't need a per-connection handle, so this just acts as a
- * pointer to return.
- */
- static int h;
-
- return &h;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
diff --git a/plugins/full/full.c b/plugins/full/full.c
index 3f5159f..cb18a48 100644
--- a/plugins/full/full.c
+++ b/plugins/full/full.c
@@ -83,9 +83,7 @@ full_config_complete (void)
static void *
full_open (int readonly)
{
- static int handle;
-
- return &handle;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
diff --git a/plugins/iso/iso.c b/plugins/iso/iso.c
index bed8486..7ed5e7a 100644
--- a/plugins/iso/iso.c
+++ b/plugins/iso/iso.c
@@ -239,12 +239,7 @@ iso_config_complete (void)
static void *
iso_open (int readonly)
{
- /* We don't need a per-connection handle, so this just acts as a
- * pointer to return.
- */
- static int h;
-
- return &h;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
diff --git a/plugins/memory/memory.c b/plugins/memory/memory.c
index 8e5c084..4013087 100644
--- a/plugins/memory/memory.c
+++ b/plugins/memory/memory.c
@@ -103,10 +103,7 @@ memory_config_complete (void)
static void *
memory_open (int readonly)
{
- /* Used only as a handle pointer. */
- static int mh;
-
- return &mh;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
#define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_ALL_REQUESTS
diff --git a/plugins/null/null.c b/plugins/null/null.c
index cee22f5..20d333e 100644
--- a/plugins/null/null.c
+++ b/plugins/null/null.c
@@ -72,9 +72,7 @@ null_config (const char *key, const char *value)
static void *
null_open (int readonly)
{
- static int handle;
-
- return &handle;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
diff --git a/plugins/partitioning/partitioning.c b/plugins/partitioning/partitioning.c
index 2889e67..43bdd7c 100644
--- a/plugins/partitioning/partitioning.c
+++ b/plugins/partitioning/partitioning.c
@@ -276,10 +276,7 @@ partitioning_config_complete (void)
static void *
partitioning_open (int readonly)
{
- /* We don't need a handle. This is a non-NULL pointer we can return. */
- static int h;
-
- return &h;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
diff --git a/plugins/pattern/pattern.c b/plugins/pattern/pattern.c
index 46b5abd..1d1b234 100644
--- a/plugins/pattern/pattern.c
+++ b/plugins/pattern/pattern.c
@@ -73,14 +73,11 @@ pattern_config (const char *key, const char *value)
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
-/* No meaning, just used as the address for the handle. */
-static int ph;
-
/* Create the per-connection handle. */
static void *
pattern_open (int readonly)
{
- return &ph;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
/* Get the disk size. */
diff --git a/plugins/random/random.c b/plugins/random/random.c
index 72caaed..9c805ab 100644
--- a/plugins/random/random.c
+++ b/plugins/random/random.c
@@ -93,14 +93,11 @@ random_config (const char *key, const char *value)
#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL
-/* No meaning, just used as the address for the handle. */
-static int rndh;
-
/* Create the per-connection handle. */
static void *
random_open (int readonly)
{
- return &rndh;
+ return NBDKIT_HANDLE_NOT_NEEDED;
}
/* Get the disk size. */
--
2.19.2
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