extstore: split write into write_request+write

write_request returns a buffer to write into, which lets us not corrupt the
active item with the hash and crc.

"technically" we can save 24 bytes per item in storage but I'll leave that
for a later optimization, in case we want to stuff more data into the header.

1 files changed, 12 insertions, 16 deletions

diff --git a/storage.c b/storage.c
index 21fd1f1..0a2d9c3 100644
--- a/storage.c
+++ b/storage.c
@@ -46,25 +46,22 @@ int lru_maintainer_store(void *storage, const int clsid) {
              * We will fill it from the header on read either way.
              */
             if (hdr_it != NULL) {
-                // N.B.: rel_time_t happens to be an unsigned int.
-                // to do this fully safely requires more refactoring.
                 // cuddle the hash value into the time field so we don't have
-                // to recalcultae it.
-                uint32_t orig_time = (uint32_t) it->time;
-                it->time = it_info.hv;
-                // Also cuddle a crc32c into the exptime field.
-                // first clear it so we get a clean crc
-                uint32_t orig_exptime = (uint32_t) it->exptime;
-                it->exptime = 0;
-                it->exptime = crc32c(0, (char*)it+24, orig_ntotal-24);
+                // to recalculate it.
+                uint32_t crc = crc32c(0, (char*)it+32, orig_ntotal-32);
                 hdr_it->it_flags |= ITEM_HDR;
-                io.buf = (void *) it;
                 io.len = orig_ntotal;
                 io.mode = OBJ_IO_WRITE;
                 // NOTE: when the item is read back in, the slab mover
                 // may see it. Important to have refcount>=2 or ~ITEM_LINKED
                 assert(it->refcount >= 2);
-                if (extstore_write(storage, 0, &io) == 0) {
+                if (extstore_write_request(storage, 0, &io) == 0) {
+                    item *buf_it = (item *) io.buf;
+                    buf_it->time = it_info.hv;
+                    buf_it->exptime = crc;
+                    // copy from past the headers + time headers.
+                    memcpy((char *)io.buf+32, (char *)it+32, io.len-32);
+                    extstore_write(storage, &io);
                     item_hdr *hdr = (item_hdr *) ITEM_data(hdr_it);
                     hdr->page_version = io.page_version;
                     hdr->page_id = io.page_id;
@@ -85,8 +82,6 @@ int lru_maintainer_store(void *storage, const int clsid) {
                     /* Failed to write for some reason, can't continue. */
                     slabs_free(hdr_it, ITEM_ntotal(hdr_it), ITEM_clsid(hdr_it));
                 }
-                it->time = orig_time;
-                it->exptime = orig_exptime;
             }
         }
         do_item_remove(it);
@@ -203,11 +198,12 @@ static void storage_compact_readback(void *storage, logger *l,
                 bool do_update = false;
                 int tries;
                 obj_io io;
-                io.buf = (void *)it;
                 io.len = ntotal;
                 io.mode = OBJ_IO_WRITE;
                 for (tries = 10; tries > 0; tries--) {
-                    if (extstore_write(storage, 1, &io) == 0) {
+                    if (extstore_write_request(storage, 1, &io) == 0) {
+                        memcpy(io.buf, it, io.len);
+                        extstore_write(storage, &io);
                         do_update = true;
                         break;
                     } else {