[Qemu-devel] [PATCH v4 6/8] hw/loader: split out load_image_gzipped_buffer()

[Laszlo Ersek <lersek@redhat.com>]

In the next patch we'd like to reuse the image decompression facility
without installing the output as a ROM at a specific guest-phys address.

In addition, expose LOAD_IMAGE_MAX_GUNZIP_BYTES, because that's a
straightforward "max_sz" argument for the new load_image_gzipped_buffer().

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
---

Notes:
    v4:
    - drop space "between function name and open parenthesis '('" [Peter]
    
    v3:
    - unchanged

 include/hw/loader.h |  9 +++++++++
 hw/core/loader.c    | 30 +++++++++++++++++++++---------
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/include/hw/loader.h b/include/hw/loader.h
index 6481639..8997620 100644
--- a/include/hw/loader.h
+++ b/include/hw/loader.h
@@ -15,8 +15,17 @@ int get_image_size(const char *filename);
 int load_image(const char *filename, uint8_t *addr); /* deprecated */
 ssize_t load_image_size(const char *filename, void *addr, size_t size);
 int load_image_targphys(const char *filename, hwaddr,
                         uint64_t max_sz);
+
+/* This is the limit on the maximum uncompressed image size that
+ * load_image_gzipped_buffer() and load_image_gzipped() will read. It prevents
+ * g_malloc() in those functions from allocating a huge amount of memory.
+ */
+#define LOAD_IMAGE_MAX_GUNZIP_BYTES (256 << 20)
+
+int load_image_gzipped_buffer(const char *filename, uint64_t max_sz,
+                              uint8_t **buffer);
 int load_image_gzipped(const char *filename, hwaddr addr, uint64_t max_sz);
 
 #define ELF_LOAD_FAILED       -1
 #define ELF_LOAD_NOT_ELF      -2
diff --git a/hw/core/loader.c b/hw/core/loader.c
index 7527fd3..f2b34da 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -613,16 +613,11 @@ int load_ramdisk(const char *filename, hwaddr addr, uint64_t max_sz)
     return load_uboot_image(filename, NULL, &addr, NULL, IH_TYPE_RAMDISK,
                             NULL, NULL);
 }
 
-/* This simply prevents g_malloc in the function below from allocating
- * a huge amount of memory, by placing a limit on the maximum
- * uncompressed image size that load_image_gzipped will read.
- */
-#define LOAD_IMAGE_MAX_GUNZIP_BYTES (256 << 20)
-
-/* Load a gzip-compressed kernel. */
-int load_image_gzipped(const char *filename, hwaddr addr, uint64_t max_sz)
+/* Load a gzip-compressed kernel to a dynamically allocated buffer. */
+int load_image_gzipped_buffer(const char *filename, uint64_t max_sz,
+                              uint8_t **buffer)
 {
     uint8_t *compressed_data = NULL;
     uint8_t *data = NULL;
     gsize len;
@@ -652,17 +647,34 @@ int load_image_gzipped(const char *filename, hwaddr addr, uint64_t max_sz)
                 filename);
         goto out;
     }
 
-    rom_add_blob_fixed(filename, data, bytes, addr);
+    /* trim to actual size and return to caller */
+    *buffer = g_realloc(data, bytes);
     ret = bytes;
+    /* ownership has been transferred to caller */
+    data = NULL;
 
  out:
     g_free(compressed_data);
     g_free(data);
     return ret;
 }
 
+/* Load a gzip-compressed kernel. */
+int load_image_gzipped(const char *filename, hwaddr addr, uint64_t max_sz)
+{
+    int bytes;
+    uint8_t *data;
+
+    bytes = load_image_gzipped_buffer(filename, max_sz, &data);
+    if (bytes != -1) {
+        rom_add_blob_fixed(filename, data, bytes, addr);
+        g_free(data);
+    }
+    return bytes;
+}
+
 /*
  * Functions for reboot-persistent memory regions.
  *  - used for vga bios and option roms.
  *  - also linux kernel (-kernel / -initrd).
-- 
1.8.3.1