From dd34949209e15ba00aff08071d2421d4079e8331 Mon Sep 17 00:00:00 2001
From: Ivan Baravy <dunkaist@gmail.com>
Date: Wed, 18 Jan 2023 19:46:44 +0000
Subject: [PATCH] qcow2: cache L1 table (speed up ~10% on my system)

---
 io.c          |  6 +++---
 vdisk/qcow2.c | 35 ++++++++++++++++++++++++++---------
 2 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/io.c b/io.c
index 4fac7e5..07edf64 100644
--- a/io.c
+++ b/io.c
@@ -25,7 +25,7 @@ io_init(int *running) {
 
 void
 io_close(struct umka_io *io) {
-	io_async_close(io->async);
+    io_async_close(io->async);
     free(io);
 }
 
@@ -44,8 +44,8 @@ ssize_t
 io_write(int fd, const void *buf, size_t count, struct umka_io *io) {
     ssize_t res;
     if (!*io->running) {
-    	res = write(fd, buf, count);
-	} else {
+        res = write(fd, buf, count);
+    } else {
         res = io_async_write(fd, buf, count, io->async);
     }
     return res;
diff --git a/vdisk/qcow2.c b/vdisk/qcow2.c
index 0387822..d38f39d 100644
--- a/vdisk/qcow2.c
+++ b/vdisk/qcow2.c
@@ -16,6 +16,9 @@
 #include "miniz/miniz.h"
 #include "io.h"
 
+#define L1_MAX_LEN (32u*1024u*1024u)
+#define L1_MAX_ENTRIES (L1_MAX_LEN / sizeof(uint64_t))
+
 struct vdisk_qcow2 {
     struct vdisk vdisk;
     int fd;
@@ -33,6 +36,7 @@ struct vdisk_qcow2 {
     off_t refcount_table_offset;
     size_t l1_size;
     uint64_t sector_idx_mask;
+    uint64_t *l1;
 };
 
 #define QCOW2_MAGIC "QFI\xfb"
@@ -93,16 +97,8 @@ qcow2_read_guest_sector(struct vdisk_qcow2 *d, uint64_t sector, uint8_t *buf) {
     uint64_t cluster_index = offset / d->cluster_size;
     uint64_t l1_index = (cluster_index) / l2_entries;
     uint64_t l2_index = (cluster_index) % l2_entries;
-    uint64_t l1_entry;
+    uint64_t l1_entry = d->l1[l1_index];
     uint64_t l2_entry;
-    uint64_t l1_entry_offset = d->l1_table_offset + l1_index*sizeof(l1_entry);
-    lseek(d->fd, l1_entry_offset, SEEK_SET);
-    if (!io_read(d->fd, &l1_entry, sizeof(l1_entry), d->vdisk.io)) {
-        fprintf(stderr, "[vdisk.qcow2] can't read from image file: %s\n",
-                strerror(errno));
-        return;
-    }
-    l1_entry = be64(&l1_entry);
 
     uint64_t l2_table_offset = l1_entry & L1_ENTRY_OFFSET_MASK;
     if (!l2_table_offset) {
@@ -162,6 +158,7 @@ vdisk_qcow2_close(void *userdata) {
     }
     free(d->cluster);
     free(d->cmp_cluster);
+    free(d->l1);
     free(d);
     COVERAGE_ON();
 }
@@ -306,5 +303,25 @@ vdisk_init_qcow2(const char *fname, struct umka_io *io) {
         return NULL;
     }
 
+    d->l1 = (uint64_t*)malloc(d->l1_size * sizeof(uint64_t));
+    if (!d->l1) {
+        fprintf(stderr, "[vdisk.qcow2] can't allocate memory: %s\n",
+                strerror(errno));
+        vdisk_qcow2_close(d);
+        return NULL;
+    }
+
+    lseek(d->fd, d->l1_table_offset, SEEK_SET);
+    if (!io_read(d->fd, d->l1, d->l1_size * sizeof(uint64_t), d->vdisk.io)) {
+        fprintf(stderr, "[vdisk.qcow2] can't read from image file: %s\n",
+                strerror(errno));
+        vdisk_qcow2_close(d);
+        return NULL;
+    }
+
+    for (uint64_t *x = d->l1; x < d->l1 + d->l1_size; x++) {
+        *x = be64(x);
+    }
+
     return (struct vdisk*)d;
 }