fellow_busy: Redo ..._body_seg_alloc in preparation for async allocations

src/fellow_cache.c

@@ -2458,7 +2458,8 @@ fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
     struct fellow_disk_seg *fds, size_t want)
 {
 	struct fellow_body_region *fbr;
-	struct buddy_off_extent *fdr;
+	struct buddy_off_extent reg, *fdr;
+	struct buddy_reqs *reqs;
 	struct fellow_cache *fc;
 	struct szc szc;
 	size_t spc;
@@ -2475,15 +2476,32 @@ fellow_busy_body_seg_alloc(struct fellow_busy *fbo,
 
 	fdr = fbr->reg;
 	if (fdr == NULL || fbr->len == fdr->size) {
+		if (FC_INJ)
+			return (0);
 
 		memset(fbr, 0, sizeof *fbr);
 
-		assert(fbo->sz_estimate > fbo->sz_dskalloc);
-		szc = fellow_busy_body_size_strategy(fbo, fbo->sz_dskalloc);
+		reqs = &fbo->bbrr.reqs;
+		reg = buddy_off_extent_nil;
 
-		fdr = fellow_busy_region_alloc(fbo, szc.sz, szc.cram);
-		if (fdr == NULL)
-			return (0);
+	  wait_dskalloc:
+		if (buddy_alloc_wait(reqs)) {
+			reg = buddy_get_next_off_extent(reqs);
+			buddy_alloc_wait_done(reqs);
+			assert(reg.off >= 0);
+		}
+
+		if (reg.off < 0) {
+			assert(fbo->sz_estimate > fbo->sz_dskalloc);
+			szc = fellow_busy_body_size_strategy(fbo,
+			    fbo->sz_dskalloc);
+			AN(buddy_req_extent(reqs, szc.sz, szc.cram));
+			goto wait_dskalloc;
+		}
+
+		// Can only fail if reg.off < 0, which can't happen
+		fdr = fellow_busy_region_commit(fbo, reg);
+		AN(fdr);
 
 		fbr->reg = fdr;
 		AZ(fbr->len);