[dm-devel] [PATCH] dm: introduce feature bitmaps

[Mikulas Patocka <mpatocka@redhat.com>]

This commit introduces feature bitmaps for dm targets and for dm core. The
dm-core bitmap is returned in the ioctl field "feature_bitmap" of the
ioctl DM_VERSION_CMD. The per-target bitmap is returned after the target
name in the ioctls DM_LIST_VERSIONS_CMD or DM_GET_TARGET_VERSION.

The bitmaps are empty so far.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-ioctl.c         |   25 ++++++++++++++++---------
 include/linux/device-mapper.h |    1 +
 include/uapi/linux/dm-ioctl.h |    9 ++++++---
 3 files changed, 23 insertions(+), 12 deletions(-)

Index: linux-2.6/include/linux/device-mapper.h
===================================================================
--- linux-2.6.orig/include/linux/device-mapper.h
+++ linux-2.6/include/linux/device-mapper.h
@@ -188,6 +188,7 @@ struct target_type {
 	const char *name;
 	struct module *module;
 	unsigned version[3];
+	uint64_t feature_bitmap;
 	dm_ctr_fn ctr;
 	dm_dtr_fn dtr;
 	dm_map_fn map;
Index: linux-2.6/include/uapi/linux/dm-ioctl.h
===================================================================
--- linux-2.6.orig/include/uapi/linux/dm-ioctl.h
+++ linux-2.6/include/uapi/linux/dm-ioctl.h
@@ -138,7 +138,10 @@ struct dm_ioctl {
 	__u32 event_nr;      	/* in/out */
 	__s32 error;		/* out */
 
-	__u64 dev;		/* in/out */
+	union {
+		__u64 dev;	/* in/out */
+		__u64 feature_bitmap;	/* out */
+	};
 
 	char name[DM_NAME_LEN];	/* device name */
 	char uuid[DM_UUID_LEN];	/* unique identifier for
@@ -286,9 +289,9 @@ enum {
 #define DM_DEV_SET_GEOMETRY	_IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR	4
-#define DM_VERSION_MINOR	48
+#define DM_VERSION_MINOR	49
 #define DM_VERSION_PATCHLEVEL	0
-#define DM_VERSION_EXTRA	"-ioctl (2022-08-24)"
+#define DM_VERSION_EXTRA	"-ioctl (2022-09-16)"
 
 /* Status bits */
 #define DM_READONLY_FLAG	(1 << 0) /* In/Out */
Index: linux-2.6/drivers/md/dm-ioctl.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-ioctl.c
+++ linux-2.6/drivers/md/dm-ioctl.c
@@ -26,6 +26,8 @@
 #define DM_MSG_PREFIX "ioctl"
 #define DM_DRIVER_EMAIL "dm-devel@redhat.com"
 
+static const __u64 feature_bitmap = 0;
+
 struct dm_file {
 	/*
 	 * poll will wait until the global event number is greater than
@@ -650,6 +652,12 @@ static int list_devices(struct file *fil
 	return 0;
 }
 
+static int version(struct file *filp, struct dm_ioctl *param, size_t param_size)
+{
+	param->feature_bitmap = feature_bitmap;
+	return 0;
+}
+
 static void list_version_get_needed(struct target_type *tt, void *needed_param)
 {
     size_t *needed = needed_param;
@@ -657,11 +665,13 @@ static void list_version_get_needed(stru
     *needed += sizeof(struct dm_target_versions);
     *needed += strlen(tt->name);
     *needed += ALIGN_MASK;
+    *needed += sizeof(__u64);
 }
 
 static void list_version_get_info(struct target_type *tt, void *param)
 {
     struct vers_iter *info = param;
+    __u64 *feature_bitmap;
 
     /* Check space - it might have changed since the first iteration */
     if ((char *)info->vers + sizeof(tt->version) + strlen(tt->name) + 1 >
@@ -680,8 +690,10 @@ static void list_version_get_info(struct
     info->vers->next = 0;
     strcpy(info->vers->name, tt->name);
 
+    feature_bitmap = align_ptr(((void *)(info->vers + 1)) + strlen(tt->name) + 1);
+    *feature_bitmap = tt->feature_bitmap;
     info->old_vers = info->vers;
-    info->vers = align_ptr(((void *) ++info->vers) + strlen(tt->name) + 1);
+    info->vers = (void *)(feature_bitmap + 1);
 }
 
 static int __list_versions(struct dm_ioctl *param, size_t param_size, const char *name)
@@ -1789,7 +1801,7 @@ static ioctl_fn lookup_ioctl(unsigned in
 		int flags;
 		ioctl_fn fn;
 	} _ioctls[] = {
-		{DM_VERSION_CMD, 0, NULL}, /* version is dealt with elsewhere */
+		{DM_VERSION_CMD, IOCTL_FLAGS_NO_PARAMS, version},
 		{DM_REMOVE_ALL_CMD, IOCTL_FLAGS_NO_PARAMS | IOCTL_FLAGS_ISSUE_GLOBAL_EVENT, remove_all},
 		{DM_LIST_DEVICES_CMD, 0, list_devices},
 
@@ -1944,7 +1956,8 @@ static int validate_params(uint cmd, str
 		param->error = 0;
 
 	/* Ignores parameters */
-	if (cmd == DM_REMOVE_ALL_CMD ||
+	if (cmd == DM_VERSION_CMD ||
+	    cmd == DM_REMOVE_ALL_CMD ||
 	    cmd == DM_LIST_DEVICES_CMD ||
 	    cmd == DM_LIST_VERSIONS_CMD)
 		return 0;
@@ -1994,12 +2007,6 @@ static int ctl_ioctl(struct file *file,
 	if (r)
 		return r;
 
-	/*
-	 * Nothing more to do for the version command.
-	 */
-	if (cmd == DM_VERSION_CMD)
-		return 0;
-
 	fn = lookup_ioctl(cmd, &ioctl_flags);
 	if (!fn) {
 		DMERR("dm_ctl_ioctl: unknown command 0x%x", command);
--
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