Improve IO error erporting

Ref #65

src/fellow_cache.c

@@ -788,6 +788,11 @@ struct fellow_cache_obj {
 	(struct fellow_cache_res){.r.err = (str), .status = fcr_ioerr}
 #define FCR_ALLOCFAIL(str) FCR_ALLOCERR(FC_ERRSTR(str))
 #define FCR_IOFAIL(str) FCR_IOERR(FC_ERRSTR(str))
+#define FCR_IOFAILHOW(str, have, want)					\
+	((have) < 0 ? errno = -(have), FCR_IOFAIL(str " error")		\
+	: ((have) == 0 ? FCR_IOFAIL(str " zero")			\
+	: ((have) < (want) ? FCR_IOFAIL(str " short")			\
+	: FCR_IOFAIL(str " other"))))
 
 const char * const fellow_cache_res_s[FCR_LIM] = {
 	[fcr_ok] = "ok",
@@ -2213,7 +2218,8 @@ fellow_cache_seglists_load(struct worker *wrk, void *priv)
 
 		ssz = fellow_io_pread_sync(fc->ffd, fdsl, next.size, next.off);
 		if (FC_INJ || ssz < 0 || (size_t)ssz != next.size) {
-			fcr = FCR_IOFAIL("disk seglist read");
+			fcr = FCR_IOFAILHOW("disk seglist read",
+				(size_t)ssz, next.size);
 			goto err;
 		}
 		err = fellow_disk_seglist_check(fdsl);
@@ -3390,7 +3396,8 @@ fellow_cache_read_complete(struct fellow_cache *fc, void *ptr, int32_t result)
 
 	assert(fcs->alloc.size <= INT32_MAX);
 	if (FC_INJ || result < (int32_t)fcs->alloc.size) {
-		fcr = FCR_IOFAIL("fcs read error");
+		fcr = FCR_IOFAILHOW("fcs read",
+		    result, (int32_t)fcs->alloc.size);
 		fcos_next = (typeof(fcos_next))FCOS_READFAIL;
 	}
 	else {
@@ -3465,8 +3472,10 @@ fellow_cache_async_write_complete(struct fellow_cache *fc,
 
 		assert(fcs->alloc.size <= INT32_MAX);
 
-		if (FC_INJ || result < (int32_t)fcs->alloc.size)
-			fcr = FCR_IOFAIL("fcs write error");
+		if (FC_INJ || result < (int32_t)fcs->alloc.size) {
+			fcr = FCR_IOFAILHOW("fcs write", result,
+			    (int32_t)fcs->alloc.size);
+		}
 		else
 			fcr = FCR_OK(fco);
 
@@ -3482,8 +3491,10 @@ fellow_cache_async_write_complete(struct fellow_cache *fc,
 		}
 	} else {
 		assert(type == FBIO_SEGLIST);
-		if (FC_INJ || result < (int32_t)fbio->u.seglist.reg.size)
-			fcr = FCR_IOFAIL("seglist write error");
+		if (FC_INJ || result < (int32_t)fbio->u.seglist.reg.size) {
+			fcr = FCR_IOFAILHOW("seglist write",
+			    result, (int32_t)fbio->u.seglist.reg.size);
+		}
 		else
 			fcr = FCR_OK(fco);
 	}