ZIL: allow zil_commit() to fail with error

This changes zil_commit() to have an int return, and updates all callers
to check it. There are no corresponding internal changes yet; it will
always return 0.

Since zil_commit() is an indication that the caller _really_ wants the
associated data to be durability stored, I've annotated it with the
__warn_unused_result__ compiler attribute (via __must_check), to emit a
warning if it's ever ussd without doing something with the return code.
I hope this will mean we never misuse it in the future.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17398

include/os/freebsd/spl/sys/debug.h

@@ -69,6 +69,10 @@
 #define	__maybe_unused __attribute__((unused))
 #endif
 
+#ifndef __must_check
+#define	__must_check __attribute__((__warn_unused_result__))
+#endif
+
 /*
  * Without this, we see warnings from objtool during normal Linux builds when
  * the kernel is built with CONFIG_STACK_VALIDATION=y:

include/os/linux/spl/sys/debug.h

@@ -69,6 +69,10 @@
 #define	__maybe_unused __attribute__((unused))
 #endif
 
+#ifndef __must_check
+#define	__must_check __attribute__((__warn_unused_result__))
+#endif
+
 /*
  * Without this, we see warnings from objtool during normal Linux builds when
  * the kernel is built with CONFIG_STACK_VALIDATION=y:

include/sys/zil.h

@@ -610,8 +610,7 @@ extern void	zil_itx_destroy(itx_t *itx);
 extern void	zil_itx_assign(zilog_t *zilog, itx_t *itx, dmu_tx_t *tx);
 
 extern void	zil_async_to_sync(zilog_t *zilog, uint64_t oid);
-extern void	zil_commit(zilog_t *zilog, uint64_t oid);
-extern void	zil_commit_impl(zilog_t *zilog, uint64_t oid);
+extern int __must_check	zil_commit(zilog_t *zilog, uint64_t oid);
 extern void	zil_remove_async(zilog_t *zilog, uint64_t oid);
 
 extern int	zil_reset(const char *osname, void *txarg);