[Libguestfs] [PATCH nbdkit 1/6] server: Add new plugin/filter .block_size callback
Richard W.M. Jones
rjones at redhat.com
Wed Feb 16 16:20:36 UTC 2022
This commit implements backend_block_size() and wires it up to a new
.block_size callback from the plugin through any filters on top.
This callback will allow plugins to pass their minimum, preferred and
maximum block size through the NBD protocol NBD_INFO_BLOCK_SIZE info
option.
The new function is not called from anywhere yet, so for the moment
this commit does nothing.
---
include/nbdkit-filter.h | 4 ++++
include/nbdkit-plugin.h | 3 +++
server/internal.h | 9 ++++++++
server/backend.c | 29 +++++++++++++++++++++++
server/filters.c | 17 ++++++++++++++
server/plugins.c | 51 +++++++++++++++++++++++++++++++++++++++++
6 files changed, 113 insertions(+)
diff --git a/include/nbdkit-filter.h b/include/nbdkit-filter.h
index 8b587d70..4c620b4f 100644
--- a/include/nbdkit-filter.h
+++ b/include/nbdkit-filter.h
@@ -84,6 +84,8 @@ struct nbdkit_next_ops {
/* These callbacks are the same as normal plugin operations. */
int64_t (*get_size) (nbdkit_next *nxdata);
const char * (*export_description) (nbdkit_next *nxdata);
+ int (*block_size) (nbdkit_next *nxdata,
+ uint32_t *minimum, uint32_t *preferred, uint32_t *maximum);
int (*can_write) (nbdkit_next *nxdata);
int (*can_flush) (nbdkit_next *nxdata);
@@ -219,6 +221,8 @@ struct nbdkit_filter {
int64_t (*get_size) (nbdkit_next *next,
void *handle);
const char * (*export_description) (nbdkit_next *next, void *handle);
+ int (*block_size) (nbdkit_next *next, void *handle,
+ uint32_t *minimum, uint32_t *preferred, uint32_t *maximum);
int (*can_write) (nbdkit_next *next,
void *handle);
diff --git a/include/nbdkit-plugin.h b/include/nbdkit-plugin.h
index 59ec11b6..50ff93df 100644
--- a/include/nbdkit-plugin.h
+++ b/include/nbdkit-plugin.h
@@ -146,6 +146,9 @@ struct nbdkit_plugin {
const char * (*export_description) (void *handle);
void (*cleanup) (void);
+
+ int (*block_size) (void *handle,
+ uint32_t *minimum, uint32_t *preferred, uint32_t *maximum);
};
NBDKIT_EXTERN_DECL (void, nbdkit_set_error, (int err));
diff --git a/server/internal.h b/server/internal.h
index f4843164..c91d196e 100644
--- a/server/internal.h
+++ b/server/internal.h
@@ -216,6 +216,9 @@ struct context {
unsigned char state; /* Bitmask of HANDLE_* values */
uint64_t exportsize;
+ uint32_t minimum_block_size;
+ uint32_t preferred_block_size;
+ uint32_t maximum_block_size;
int can_write;
int can_flush;
int is_rotational;
@@ -368,6 +371,8 @@ struct backend {
const char *(*export_description) (struct context *);
int64_t (*get_size) (struct context *);
+ int (*block_size) (struct context *,
+ uint32_t *minimum, uint32_t *preferred, uint32_t *maximum);
int (*can_write) (struct context *);
int (*can_flush) (struct context *);
int (*is_rotational) (struct context *);
@@ -433,6 +438,10 @@ extern const char *backend_export_description (struct context *c)
__attribute__((__nonnull__ (1)));
extern int64_t backend_get_size (struct context *c)
__attribute__((__nonnull__ (1)));
+extern int backend_block_size (struct context *c,
+ uint32_t *minimum, uint32_t *preferred,
+ uint32_t *maximum)
+ __attribute__((__nonnull__ (1, 2, 3, 4)));
extern int backend_can_write (struct context *c)
__attribute__((__nonnull__ (1)));
extern int backend_can_flush (struct context *c)
diff --git a/server/backend.c b/server/backend.c
index 1bb3dac9..7d46b99d 100644
--- a/server/backend.c
+++ b/server/backend.c
@@ -214,6 +214,7 @@ static struct nbdkit_next_ops next_ops = {
.finalize = backend_finalize,
.export_description = backend_export_description,
.get_size = backend_get_size,
+ .block_size = backend_block_size,
.can_write = backend_can_write,
.can_flush = backend_can_flush,
.is_rotational = backend_is_rotational,
@@ -265,6 +266,7 @@ backend_open (struct backend *b, int readonly, const char *exportname,
c->conn = shared ? NULL : conn;
c->state = 0;
c->exportsize = -1;
+ c->minimum_block_size = c->preferred_block_size = c->maximum_block_size = -1;
c->can_write = readonly ? 0 : -1;
c->can_flush = -1;
c->is_rotational = -1;
@@ -418,6 +420,33 @@ backend_get_size (struct context *c)
return c->exportsize;
}
+int
+backend_block_size (struct context *c,
+ uint32_t *minimum, uint32_t *preferred, uint32_t *maximum)
+{
+ PUSH_CONTEXT_FOR_SCOPE (c);
+ struct backend *b = c->b;
+ int r;
+
+ assert (c->handle && (c->state & HANDLE_CONNECTED));
+ if (c->minimum_block_size != -1) {
+ *minimum = c->minimum_block_size;
+ *preferred = c->preferred_block_size;
+ *maximum = c->maximum_block_size;
+ return 0;
+ }
+ else {
+ controlpath_debug ("%s: block_size", b->name);
+ r = b->block_size (c, minimum, preferred, maximum);
+ if (r == 0) {
+ c->minimum_block_size = *minimum;
+ c->preferred_block_size = *preferred;
+ c->maximum_block_size = *maximum;
+ }
+ return r;
+ }
+}
+
int
backend_can_write (struct context *c)
{
diff --git a/server/filters.c b/server/filters.c
index 93ee55f0..ae7e1a56 100644
--- a/server/filters.c
+++ b/server/filters.c
@@ -358,6 +358,22 @@ filter_get_size (struct context *c)
return backend_get_size (c_next);
}
+static int
+filter_block_size (struct context *c,
+ uint32_t *minimum, uint32_t *preferred, uint32_t *maximum)
+{
+ struct backend *b = c->b;
+ struct backend_filter *f = container_of (b, struct backend_filter, backend);
+ struct context *c_next = c->c_next;
+
+ if (f->filter.block_size)
+ return f->filter.block_size (c_next, c->handle,
+ minimum, preferred, maximum);
+ else
+ return backend_block_size (c_next,
+ minimum, preferred, maximum);
+}
+
static int
filter_can_write (struct context *c)
{
@@ -621,6 +637,7 @@ static struct backend filter_functions = {
.close = filter_close,
.export_description = filter_export_description,
.get_size = filter_get_size,
+ .block_size = filter_block_size,
.can_write = filter_can_write,
.can_flush = filter_can_flush,
.is_rotational = filter_is_rotational,
diff --git a/server/plugins.c b/server/plugins.c
index b633c107..34d7a10c 100644
--- a/server/plugins.c
+++ b/server/plugins.c
@@ -46,6 +46,7 @@
#include "internal.h"
#include "minmax.h"
+#include "ispowerof2.h"
/* We extend the generic backend struct with extra fields relating
* to this plugin.
@@ -173,6 +174,7 @@ plugin_dump_fields (struct backend *b)
HAS (close);
HAS (export_description);
HAS (get_size);
+ HAS (block_size);
HAS (can_write);
HAS (can_flush);
HAS (is_rotational);
@@ -408,6 +410,54 @@ plugin_get_size (struct context *c)
return p->plugin.get_size (c->handle);
}
+static int
+plugin_block_size (struct context *c,
+ uint32_t *minimum, uint32_t *preferred, uint32_t *maximum)
+{
+ struct backend *b = c->b;
+ struct backend_plugin *p = container_of (b, struct backend_plugin, backend);
+ int r;
+
+ if (p->plugin.block_size) {
+ r = p->plugin.block_size (c->handle, minimum, preferred, maximum);
+ if (r == 0) {
+ /* To make scripting easier, it's permitted to set
+ * minimum = preferred = maximum = 0 and return 0.
+ * That means "no information", and works the same
+ * way as the else clause below.
+ */
+ if (*minimum == 0 && *preferred == 0 && *maximum == 0)
+ return 0;
+
+ if (*minimum < 1) {
+ nbdkit_error ("plugin must set minimum block size >= 1");
+ r = -1;
+ }
+ if (! is_power_of_2 (*minimum)) {
+ nbdkit_error ("plugin must set minimum block size to a power of 2");
+ r = -1;
+ }
+ if (*minimum > *preferred || *preferred > *maximum) {
+ nbdkit_error ("plugin must set minimum block size "
+ "<= preferred <= maximum");
+ r = -1;
+ }
+ /* XXX Other checks should be performed here:
+ * preferred and maximum should be multiples of the minimum.
+ */
+ }
+ return r;
+ }
+ else {
+ /* If there is no .block_size call then return minimum = preferred
+ * = maximum = 0, which is a sentinel meaning don't send the
+ * NBD_INFO_BLOCK_SIZE message.
+ */
+ *minimum = *preferred = *maximum = 0;
+ return 0;
+ }
+}
+
static int
normalize_bool (int value)
{
@@ -824,6 +874,7 @@ static struct backend plugin_functions = {
.close = plugin_close,
.export_description = plugin_export_description,
.get_size = plugin_get_size,
+ .block_size = plugin_block_size,
.can_write = plugin_can_write,
.can_flush = plugin_can_flush,
.is_rotational = plugin_is_rotational,
--
2.35.1
More information about the Libguestfs
mailing list