Use fallthrough macro

As of the Linux 5.9 kernel a fallthrough macro has been added which
should be used to anotate all intentional fallthrough paths.  Once
all of the kernel code paths have been updated to use fallthrough
the -Wimplicit-fallthrough option will because the default.  To
avoid warnings in the OpenZFS code base when this happens apply
the fallthrough macro.

Additional reading: https://lwn.net/Articles/794944/

Reviewed-by: Tony Nguyen <[email protected]>
Reviewed-by: George Melikov <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #12441

18 files changed, 29 insertions, 27 deletions

diff --git a/module/icp/core/kcf_prov_tabs.c b/module/icp/core/kcf_prov_tabs.c
index 94e6937bc..9d303d022 100644
--- a/module/icp/core/kcf_prov_tabs.c
+++ b/module/icp/core/kcf_prov_tabs.c
@@ -377,7 +377,7 @@ kcf_provider_zero_refcnt(kcf_provider_desc_t *desc)
 			mutex_exit(&desc->pd_lock);
 			break;
 		}
-		/* FALLTHRU */
+		fallthrough;
 
 	case CRYPTO_HW_PROVIDER:
 	case CRYPTO_LOGICAL_PROVIDER:
diff --git a/module/icp/io/aes.c b/module/icp/io/aes.c
index e540af447..c47c7567b 100644
--- a/module/icp/io/aes.c
+++ b/module/icp/io/aes.c
@@ -976,7 +976,7 @@ aes_encrypt_atomic(crypto_provider_handle_t provider,
 	case AES_GMAC_MECH_INFO_TYPE:
 		if (plaintext->cd_length != 0)
 			return (CRYPTO_ARGUMENTS_BAD);
-		/* FALLTHRU */
+		fallthrough;
 	case AES_GCM_MECH_INFO_TYPE:
 		length_needed = plaintext->cd_length + aes_ctx.ac_tag_len;
 		break;
diff --git a/module/lua/lcode.c b/module/lua/lcode.c
index ae9a3d91d..4d88c792a 100644
--- a/module/lua/lcode.c
+++ b/module/lua/lcode.c
@@ -8,6 +8,10 @@
 #define lcode_c
 #define LUA_CORE
 
+#if defined(HAVE_IMPLICIT_FALLTHROUGH)
+#pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
+#endif
+
 #include <sys/lua/lua.h>
 
 #include "lcode.h"
diff --git a/module/lua/lgc.c b/module/lua/lgc.c
index 55feb2411..227ad723a 100644
--- a/module/lua/lgc.c
+++ b/module/lua/lgc.c
@@ -676,7 +676,7 @@ static void freeobj (lua_State *L, GCObject *o) {
     case LUA_TUSERDATA: luaM_freemem(L, o, sizeudata(gco2u(o))); break;
     case LUA_TSHRSTR:
       G(L)->strt.nuse--;
-      /* FALLTHROUGH */
+      fallthrough;
     case LUA_TLNGSTR: {
       luaM_freemem(L, o, sizestring(gco2ts(o)));
       break;
diff --git a/module/lua/llex.c b/module/lua/llex.c
index 50c301f59..f2c9bf826 100644
--- a/module/lua/llex.c
+++ b/module/lua/llex.c
@@ -477,7 +477,7 @@ static int llex (LexState *ls, SemInfo *seminfo) {
         else if (!lisdigit(ls->current)) return '.';
         /* else go through */
       }
-      /* FALLTHROUGH */
+        fallthrough;
       case '0': case '1': case '2': case '3': case '4':
       case '5': case '6': case '7': case '8': case '9': {
         read_numeral(ls, seminfo);
diff --git a/module/lua/lstrlib.c b/module/lua/lstrlib.c
index 12027757b..46e3d8fb3 100644
--- a/module/lua/lstrlib.c
+++ b/module/lua/lstrlib.c
@@ -501,7 +501,7 @@ static const char *match (MatchState *ms, const char *s, const char *p) {
             }
             case '+':  /* 1 or more repetitions */
               s++;  /* 1 match already done */
-              /* FALLTHROUGH */
+              fallthrough;
             case '*':  /* 0 or more repetitions */
               s = max_expand(ms, s, p, ep);
               break;
diff --git a/module/lua/ltable.c b/module/lua/ltable.c
index f60418721..f6872babc 100644
--- a/module/lua/ltable.c
+++ b/module/lua/ltable.c
@@ -492,7 +492,7 @@ const TValue *luaH_get (Table *t, const TValue *key) {
         return luaH_getint(t, k);  /* use specialized version */
       /* else go through */
     }
-    /* FALLTHROUGH */
+      fallthrough;
     default: {
       Node *n = mainposition(t, key);
       do {  /* check whether `key' is somewhere in the chain */
diff --git a/module/os/freebsd/zfs/zfs_acl.c b/module/os/freebsd/zfs/zfs_acl.c
index 9b4108630..ae758bcef 100644
--- a/module/os/freebsd/zfs/zfs_acl.c
+++ b/module/os/freebsd/zfs/zfs_acl.c
@@ -269,7 +269,7 @@ zfs_ace_fuid_size(void *acep)
 		    entry_type == OWNING_GROUP ||
 		    entry_type == ACE_EVERYONE)
 			return (sizeof (zfs_ace_hdr_t));
-		/*FALLTHROUGH*/
+		fallthrough;
 	default:
 		return (sizeof (zfs_ace_t));
 	}
@@ -2153,7 +2153,7 @@ zfs_zaccess_aces_check(znode_t *zp, uint32_t *working_mode,
 			break;
 		case OWNING_GROUP:
 			who = gowner;
-			/*FALLTHROUGH*/
+			fallthrough;
 		case ACE_IDENTIFIER_GROUP:
 			checkit = zfs_groupmember(zfsvfs, who, cr);
 			break;
diff --git a/module/os/freebsd/zfs/zfs_vnops_os.c b/module/os/freebsd/zfs/zfs_vnops_os.c
index 4672b9c2b..be8253044 100644
--- a/module/os/freebsd/zfs/zfs_vnops_os.c
+++ b/module/os/freebsd/zfs/zfs_vnops_os.c
@@ -974,7 +974,7 @@ zfs_lookup(vnode_t *dvp, const char *nm, vnode_t **vpp,
 				cnp->cn_flags |= SAVENAME;
 				break;
 			}
-			/* FALLTHROUGH */
+			fallthrough;
 		case DELETE:
 			if (error == 0)
 				cnp->cn_flags |= SAVENAME;
diff --git a/module/os/linux/zfs/zfs_acl.c b/module/os/linux/zfs/zfs_acl.c
index f8bf55f75..cf37aecf8 100644
--- a/module/os/linux/zfs/zfs_acl.c
+++ b/module/os/linux/zfs/zfs_acl.c
@@ -269,7 +269,7 @@ zfs_ace_fuid_size(void *acep)
 		    entry_type == OWNING_GROUP ||
 		    entry_type == ACE_EVERYONE)
 			return (sizeof (zfs_ace_hdr_t));
-		/*FALLTHROUGH*/
+		fallthrough;
 	default:
 		return (sizeof (zfs_ace_t));
 	}
@@ -2317,7 +2317,7 @@ zfs_zaccess_aces_check(znode_t *zp, uint32_t *working_mode,
 			break;
 		case OWNING_GROUP:
 			who = gowner;
-			/*FALLTHROUGH*/
+			fallthrough;
 		case ACE_IDENTIFIER_GROUP:
 			checkit = zfs_groupmember(zfsvfs, who, cr);
 			break;
diff --git a/module/os/linux/zfs/zfs_znode.c b/module/os/linux/zfs/zfs_znode.c
index c841cc0fc..cd80049df 100644
--- a/module/os/linux/zfs/zfs_znode.c
+++ b/module/os/linux/zfs/zfs_znode.c
@@ -430,7 +430,7 @@ zfs_inode_set_ops(zfsvfs_t *zfsvfs, struct inode *ip)
 	case S_IFBLK:
 		(void) sa_lookup(ITOZ(ip)->z_sa_hdl, SA_ZPL_RDEV(zfsvfs), &rdev,
 		    sizeof (rdev));
-		/*FALLTHROUGH*/
+		fallthrough;
 	case S_IFIFO:
 	case S_IFSOCK:
 		init_special_inode(ip, ip->i_mode, rdev);
diff --git a/module/zfs/abd.c b/module/zfs/abd.c
index cc2d3575d..03a7b1e03 100644
--- a/module/zfs/abd.c
+++ b/module/zfs/abd.c
@@ -1066,10 +1066,10 @@ abd_raidz_gen_iterate(abd_t **cabds, abd_t *dabd,
 		switch (parity) {
 			case 3:
 				len = MIN(caiters[2].iter_mapsize, len);
-				/* falls through */
+				fallthrough;
 			case 2:
 				len = MIN(caiters[1].iter_mapsize, len);
-				/* falls through */
+				fallthrough;
 			case 1:
 				len = MIN(caiters[0].iter_mapsize, len);
 		}
@@ -1179,11 +1179,11 @@ abd_raidz_rec_iterate(abd_t **cabds, abd_t **tabds,
 			case 3:
 				len = MIN(xiters[2].iter_mapsize, len);
 				len = MIN(citers[2].iter_mapsize, len);
-				/* falls through */
+				fallthrough;
 			case 2:
 				len = MIN(xiters[1].iter_mapsize, len);
 				len = MIN(citers[1].iter_mapsize, len);
-				/* falls through */
+				fallthrough;
 			case 1:
 				len = MIN(xiters[0].iter_mapsize, len);
 				len = MIN(citers[0].iter_mapsize, len);
diff --git a/module/zfs/dsl_prop.c b/module/zfs/dsl_prop.c
index f6ff9ae47..dfa04d768 100644
--- a/module/zfs/dsl_prop.c
+++ b/module/zfs/dsl_prop.c
@@ -749,7 +749,7 @@ dsl_prop_set_sync_impl(dsl_dataset_t *ds, const char *propname,
 		ASSERT(err == 0 || err == ENOENT);
 		err = zap_remove(mos, zapobj, inheritstr, tx);
 		ASSERT(err == 0 || err == ENOENT);
-		/* FALLTHRU */
+		fallthrough;
 	case (ZPROP_SRC_NONE | ZPROP_SRC_RECEIVED):
 		/*
 		 * remove propname$recvd
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 55870bee4..a02fd198b 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -9710,7 +9710,7 @@ spa_activity_in_progress(spa_t *spa, zpool_wait_activity_t activity,
 	case ZPOOL_WAIT_RESILVER:
 		if ((*in_progress = vdev_rebuild_active(spa->spa_root_vdev)))
 			break;
-		/* fall through */
+		fallthrough;
 	case ZPOOL_WAIT_SCRUB:
 	{
 		boolean_t scanning, paused, is_scrub;
diff --git a/module/zfs/vdev_label.c b/module/zfs/vdev_label.c
index 04202a9f8..ec6bbc6fc 100644
--- a/module/zfs/vdev_label.c
+++ b/module/zfs/vdev_label.c
@@ -1287,7 +1287,7 @@ vdev_label_read_bootenv(vdev_t *rvd, nvlist_t *bootenv)
 				nvlist_free(config);
 				break;
 			}
-			/* FALLTHROUGH */
+			fallthrough;
 		default:
 			/* Check for FreeBSD zfs bootonce command string */
 			buf = abd_to_buf(abd);
diff --git a/module/zfs/vdev_raidz_math_scalar.c b/module/zfs/vdev_raidz_math_scalar.c
index cd742e146..9e9c15ff4 100644
--- a/module/zfs/vdev_raidz_math_scalar.c
+++ b/module/zfs/vdev_raidz_math_scalar.c
@@ -142,7 +142,7 @@ static const struct {
 		a.b[6] = mul_lt[a.b[6]];				\
 		a.b[5] = mul_lt[a.b[5]];				\
 		a.b[4] = mul_lt[a.b[4]];				\
-		/* falls through */					\
+		fallthrough;						\
 	case 4:								\
 		a.b[3] = mul_lt[a.b[3]];				\
 		a.b[2] = mul_lt[a.b[2]];				\
diff --git a/module/zfs/zfs_replay.c b/module/zfs/zfs_replay.c
index cba5e8c9c..f3d209f1f 100644
--- a/module/zfs/zfs_replay.c
+++ b/module/zfs/zfs_replay.c
@@ -362,7 +362,7 @@ zfs_replay_create_acl(void *arg1, void *arg2, boolean_t byteswap)
 		zfsvfs->z_fuid_replay = zfs_replay_fuids(fuidstart,
 		    (void *)&name, lracl->lr_fuidcnt, lracl->lr_domcnt,
 		    lr->lr_uid, lr->lr_gid);
-		/*FALLTHROUGH*/
+		fallthrough;
 	case TX_CREATE_ACL_ATTR:
 		if (name == NULL) {
 			lrattr = (lr_attr_t *)(caddr_t)(lracl + 1);
@@ -394,7 +394,7 @@ zfs_replay_create_acl(void *arg1, void *arg2, boolean_t byteswap)
 		zfsvfs->z_fuid_replay = zfs_replay_fuids(fuidstart,
 		    (void *)&name, lracl->lr_fuidcnt, lracl->lr_domcnt,
 		    lr->lr_uid, lr->lr_gid);
-		/*FALLTHROUGH*/
+		fallthrough;
 	case TX_MKDIR_ACL_ATTR:
 		if (name == NULL) {
 			lrattr = (lr_attr_t *)(caddr_t)(lracl + 1);
@@ -519,8 +519,7 @@ zfs_replay_create(void *arg1, void *arg2, boolean_t byteswap)
 		    zfs_replay_fuid_domain(start, &start,
 		    lr->lr_uid, lr->lr_gid);
 		name = (char *)start;
-
-		/*FALLTHROUGH*/
+		fallthrough;
 	case TX_CREATE:
 		if (name == NULL)
 			name = (char *)start;
@@ -537,8 +536,7 @@ zfs_replay_create(void *arg1, void *arg2, boolean_t byteswap)
 		    zfs_replay_fuid_domain(start, &start,
 		    lr->lr_uid, lr->lr_gid);
 		name = (char *)start;
-
-		/*FALLTHROUGH*/
+		fallthrough;
 	case TX_MKDIR:
 		if (name == NULL)
 			name = (char *)(lr + 1);
diff --git a/module/zfs/zio_compress.c b/module/zfs/zio_compress.c
index 33602bd47..1ff1e76d7 100644
--- a/module/zfs/zio_compress.c
+++ b/module/zfs/zio_compress.c
@@ -214,7 +214,7 @@ zio_compress_to_feature(enum zio_compress comp)
 	case ZIO_COMPRESS_ZSTD:
 		return (SPA_FEATURE_ZSTD_COMPRESS);
 	default:
-		/* fallthru */;
+		break;
 	}
 	return (SPA_FEATURE_NONE);
 }