[Qemu-devel] [PATCH v2 08/17] block: add flag to indicate that no I/O will be performed

["Daniel P. Berrange" <berrange@redhat.com>]

When opening an image it is useful to know whether the caller
intends to perform I/O on the image or not. In the case of
encrypted images this will allow the block driver to avoid
having to prompt for decryption keys when we merely want to
query header metadata about the image. eg qemu-img info

This flag is enforced at the top level only, since even if
we don't want todo I/O on the 'qcow2' file payload, the
underlying 'file' driver will still need todo I/O to read
the qcow2 header, for example.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 block.c               |  5 +++--
 block/io.c            |  2 ++
 include/block/block.h |  1 +
 qemu-img.c            | 33 +++++++++++++++++----------------
 4 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/block.c b/block.c
index 54c37f9..0806d4f 100644
--- a/block.c
+++ b/block.c
@@ -719,7 +719,8 @@ static void bdrv_inherited_options(int *child_flags, QDict *child_options,
     flags |= BDRV_O_UNMAP;
 
     /* Clear flags that only apply to the top layer */
-    flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_COPY_ON_READ);
+    flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_COPY_ON_READ |
+               BDRV_O_NO_IO);
 
     *child_flags = flags;
 }
@@ -739,7 +740,7 @@ static void bdrv_inherited_fmt_options(int *child_flags, QDict *child_options,
     child_file.inherit_options(child_flags, child_options,
                                parent_flags, parent_options);
 
-    *child_flags &= ~BDRV_O_PROTOCOL;
+    *child_flags &= ~(BDRV_O_PROTOCOL | BDRV_O_NO_IO);
 }
 
 const BdrvChildRole child_format = {
diff --git a/block/io.c b/block/io.c
index 63e3678..ebd26cd 100644
--- a/block/io.c
+++ b/block/io.c
@@ -859,6 +859,7 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
     assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
     assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
     assert(!qiov || bytes == qiov->size);
+    assert((bs->open_flags & BDRV_O_NO_IO) == 0);
 
     /* Handle Copy on Read and associated serialisation */
     if (flags & BDRV_REQ_COPY_ON_READ) {
@@ -1145,6 +1146,7 @@ static int coroutine_fn bdrv_aligned_pwritev(BlockDriverState *bs,
     assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
     assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
     assert(!qiov || bytes == qiov->size);
+    assert((bs->open_flags & BDRV_O_NO_IO) == 0);
 
     waited = wait_serialising_requests(req);
     assert(!waited || !req->serialising);
diff --git a/include/block/block.h b/include/block/block.h
index c96923d..73ffbd5 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -91,6 +91,7 @@ typedef struct HDGeometry {
 #define BDRV_O_PROTOCOL    0x8000  /* if no block driver is explicitly given:
                                       select an appropriate protocol driver,
                                       ignoring the format layer */
+#define BDRV_O_NO_IO       0x10000 /* don't initialize for I/O */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH)
 
diff --git a/qemu-img.c b/qemu-img.c
index 4052aba..e79f29b 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -267,7 +267,7 @@ static BlockBackend *img_open_opts(const char *id,
 
 static BlockBackend *img_open_file(const char *id, const char *filename,
                                    const char *fmt, int flags,
-                                   bool require_io, bool quiet)
+                                   bool quiet)
 {
     BlockBackend *blk;
     BlockDriverState *bs;
@@ -287,7 +287,7 @@ static BlockBackend *img_open_file(const char *id, const char *filename,
     }
 
     bs = blk_bs(blk);
-    if (bdrv_is_encrypted(bs) && require_io) {
+    if (bdrv_is_encrypted(bs) && !(flags & BDRV_O_NO_IO)) {
         qprintf(quiet, "Disk image '%s' is encrypted.\n", filename);
         if (qemu_read_password(password, sizeof(password)) < 0) {
             error_report("No password given");
@@ -680,7 +680,7 @@ static int img_check(int argc, char **argv)
         }
         blk = img_open_opts("image", opts, flags);
     } else {
-        blk = img_open_file("image", filename, fmt, flags, true, quiet);
+        blk = img_open_file("image", filename, fmt, flags, quiet);
     }
     if (!blk) {
         return 1;
@@ -885,7 +885,7 @@ static int img_commit(int argc, char **argv)
         }
         blk = img_open_opts("image", opts, flags);
     } else {
-        blk = img_open_file("image", filename, fmt, flags, true, quiet);
+        blk = img_open_file("image", filename, fmt, flags, quiet);
     }
     if (!blk) {
         return 1;
@@ -1247,13 +1247,13 @@ static int img_compare(int argc, char **argv)
             goto out3;
         }
     } else {
-        blk1 = img_open_file("image_1", filename1, fmt1, flags, true, quiet);
+        blk1 = img_open_file("image_1", filename1, fmt1, flags, quiet);
         if (!blk1) {
             ret = 2;
             goto out3;
         }
 
-        blk2 = img_open_file("image_2", filename2, fmt2, flags, true, quiet);
+        blk2 = img_open_file("image_2", filename2, fmt2, flags, quiet);
         if (!blk2) {
             ret = 2;
             goto out2;
@@ -1933,7 +1933,7 @@ static int img_convert(int argc, char **argv)
             blk[bs_i] = img_open_opts(id, opts, src_flags);
         } else {
             blk[bs_i] = img_open_file(id, argv[optind + bs_i], fmt, src_flags,
-                                      true, quiet);
+                                      quiet);
         }
         g_free(id);
         if (!blk[bs_i]) {
@@ -2080,7 +2080,7 @@ static int img_convert(int argc, char **argv)
      * the bdrv_create() call which takes different params
      */
     out_blk = img_open_file("target", out_filename,
-                            out_fmt, flags, true, quiet);
+                            out_fmt, flags, quiet);
     if (!out_blk) {
         ret = -1;
         goto out;
@@ -2284,12 +2284,13 @@ static ImageInfoList *collect_image_info_list(bool image_opts,
                 goto err;
             }
             blk = img_open_opts("image", opts,
-                                BDRV_O_FLAGS | BDRV_O_NO_BACKING);
+                                BDRV_O_FLAGS | BDRV_O_NO_BACKING |
+                                BDRV_O_NO_IO);
             opts = NULL;
         } else {
             blk = img_open_file("image", filename, fmt,
-                                BDRV_O_FLAGS | BDRV_O_NO_BACKING,
-                                false, false);
+                                BDRV_O_FLAGS | BDRV_O_NO_BACKING |
+                                BDRV_O_NO_IO, false);
         }
         if (!blk) {
             goto err;
@@ -2606,7 +2607,7 @@ static int img_map(int argc, char **argv)
         }
         blk = img_open_opts("image", opts, BDRV_O_FLAGS);
     } else {
-        blk = img_open_file("image", filename, fmt, BDRV_O_FLAGS, true, false);
+        blk = img_open_file("image", filename, fmt, BDRV_O_FLAGS, false);
     }
     if (!blk) {
         return 1;
@@ -2763,7 +2764,7 @@ static int img_snapshot(int argc, char **argv)
         }
         blk = img_open_opts("image", opts, bdrv_oflags);
     } else {
-        blk = img_open_file("image", filename, NULL, bdrv_oflags, true, quiet);
+        blk = img_open_file("image", filename, NULL, bdrv_oflags, quiet);
     }
     if (!blk) {
         return 1;
@@ -2948,7 +2949,7 @@ static int img_rebase(int argc, char **argv)
         }
         blk = img_open_opts("image", opts, flags);
     } else {
-        blk = img_open_file("image", filename, fmt, flags, true, quiet);
+        blk = img_open_file("image", filename, fmt, flags, quiet);
     }
     if (!blk) {
         ret = -1;
@@ -3302,7 +3303,7 @@ static int img_resize(int argc, char **argv)
         blk = img_open_opts("image", opts, BDRV_O_FLAGS | BDRV_O_RDWR);
     } else {
         blk = img_open_file("image", filename, fmt, BDRV_O_FLAGS | BDRV_O_RDWR,
-                            true, quiet);
+                            quiet);
     }
     if (!blk) {
         ret = -1;
@@ -3473,7 +3474,7 @@ static int img_amend(int argc, char **argv)
         }
         blk = img_open_opts("image", opts, flags);
     } else {
-        blk = img_open_file("image", filename, fmt, flags, true, quiet);
+        blk = img_open_file("image", filename, fmt, flags, quiet);
     }
     if (!blk) {
         ret = -1;
-- 
2.5.0