block: add flag to indicate that no I/O will be performed

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.

Reviewed-by: Eric Blake <[email protected]>
Signed-off-by: Daniel P. Berrange <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>

diff --git a/block.c b/block.c
index 4158a3a36f11e9c56ab592f1503386073974f17a..b4bec4b1e689a678ec1debaa5731e7d056212ce1 100644 (file)
--- a/block.c
+++ b/block.c
@@ -702,7 +702,8 @@ 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;
 }
@@ -722,7 +723,7 @@ 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 c2611e53c86b38ceb64928424c9d19d7ee16472b..4520cab852a4bd5e37d0f53588bd50c170944d6b 100644 (file)
--- a/block/io.c
+++ b/block/io.c
@@ -844,6 +844,7 @@ 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) {
@@ -1130,6 +1131,7 @@ 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 a48ad49397705c5192151d461f6b429ede54e7c3..c236e1d8131e2c506009ca302377c53185d3b028 100644 (file)
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -93,6 +93,7 @@ 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 bd93d0a774d534241983147a56cefcc1e1d6be0e..9e3ac9c1a871894fd8b5a3e01ed1df6e805a18ec 100644 (file)
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -225,13 +225,13 @@ static int print_block_option_help(const char *filename, const char *fmt)
 
 
 static int img_open_password(BlockBackend *blk, const char *filename,
-                             bool require_io, bool quiet)
+                             int flags, bool quiet)
 {
     BlockDriverState *bs;
     char password[256];
 
     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");
@@ -248,7 +248,7 @@ static int img_open_password(BlockBackend *blk, const char *filename,
 
 static BlockBackend *img_open_opts(const char *optstr,
                                    QemuOpts *opts, int flags,
-                                   bool require_io, bool quiet)
+                                   bool quiet)
 {
     QDict *options;
     Error *local_err = NULL;
@@ -260,7 +260,7 @@ static BlockBackend *img_open_opts(const char *optstr,
         return NULL;
     }
 
-    if (img_open_password(blk, optstr, require_io, quiet) < 0) {
+    if (img_open_password(blk, optstr, flags, quiet) < 0) {
         blk_unref(blk);
         return NULL;
     }
@@ -269,7 +269,7 @@ static BlockBackend *img_open_opts(const char *optstr,
 
 static BlockBackend *img_open_file(const char *filename,
                                    const char *fmt, int flags,
-                                   bool require_io, bool quiet)
+                                   bool quiet)
 {
     BlockBackend *blk;
     Error *local_err = NULL;
@@ -286,7 +286,7 @@ static BlockBackend *img_open_file(const char *filename,
         return NULL;
     }
 
-    if (img_open_password(blk, filename, require_io, quiet) < 0) {
+    if (img_open_password(blk, filename, flags, quiet) < 0) {
         blk_unref(blk);
         return NULL;
     }
@@ -297,7 +297,7 @@ static BlockBackend *img_open_file(const char *filename,
 static BlockBackend *img_open(bool image_opts,
                               const char *filename,
                               const char *fmt, int flags,
-                              bool require_io, bool quiet)
+                              bool quiet)
 {
     BlockBackend *blk;
     if (image_opts) {
@@ -311,9 +311,9 @@ static BlockBackend *img_open(bool image_opts,
         if (!opts) {
             return NULL;
         }
-        blk = img_open_opts(filename, opts, flags, true, quiet);
+        blk = img_open_opts(filename, opts, flags, quiet);
     } else {
-        blk = img_open_file(filename, fmt, flags, true, quiet);
+        blk = img_open_file(filename, fmt, flags, quiet);
     }
     return blk;
 }
@@ -685,7 +685,7 @@ static int img_check(int argc, char **argv)
         return 1;
     }
 
-    blk = img_open(image_opts, filename, fmt, flags, true, quiet);
+    blk = img_open(image_opts, filename, fmt, flags, quiet);
     if (!blk) {
         return 1;
     }
@@ -877,7 +877,7 @@ static int img_commit(int argc, char **argv)
         return 1;
     }
 
-    blk = img_open(image_opts, filename, fmt, flags, true, quiet);
+    blk = img_open(image_opts, filename, fmt, flags, quiet);
     if (!blk) {
         return 1;
     }
@@ -1211,13 +1211,13 @@ static int img_compare(int argc, char **argv)
         goto out3;
     }
 
-    blk1 = img_open(image_opts, filename1, fmt1, flags, true, quiet);
+    blk1 = img_open(image_opts, filename1, fmt1, flags, quiet);
     if (!blk1) {
         ret = 2;
         goto out3;
     }
 
-    blk2 = img_open(image_opts, filename2, fmt2, flags, true, quiet);
+    blk2 = img_open(image_opts, filename2, fmt2, flags, quiet);
     if (!blk2) {
         ret = 2;
         goto out2;
@@ -1899,7 +1899,7 @@ static int img_convert(int argc, char **argv)
     total_sectors = 0;
     for (bs_i = 0; bs_i < bs_n; bs_i++) {
         blk[bs_i] = img_open(image_opts, argv[optind + bs_i],
-                             fmt, src_flags, true, quiet);
+                             fmt, src_flags, quiet);
         if (!blk[bs_i]) {
             ret = -1;
             goto out;
@@ -2044,7 +2044,7 @@ static int img_convert(int argc, char **argv)
      * the bdrv_create() call which takes different params.
      * Not critical right now, so fix can wait...
      */
-    out_blk = img_open_file(out_filename, out_fmt, flags, true, quiet);
+    out_blk = img_open_file(out_filename, out_fmt, flags, quiet);
     if (!out_blk) {
         ret = -1;
         goto out;
@@ -2236,8 +2236,8 @@ static ImageInfoList *collect_image_info_list(bool image_opts,
         g_hash_table_insert(filenames, (gpointer)filename, NULL);
 
         blk = img_open(image_opts, 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;
         }
@@ -2567,7 +2567,7 @@ static int img_map(int argc, char **argv)
         return 1;
     }
 
-    blk = img_open(image_opts, filename, fmt, BDRV_O_FLAGS, true, false);
+    blk = img_open(image_opts, filename, fmt, BDRV_O_FLAGS, false);
     if (!blk) {
         return 1;
     }
@@ -2712,7 +2712,7 @@ static int img_snapshot(int argc, char **argv)
     }
 
     /* Open the image */
-    blk = img_open(image_opts, filename, NULL, bdrv_oflags, true, quiet);
+    blk = img_open(image_opts, filename, NULL, bdrv_oflags, quiet);
     if (!blk) {
         return 1;
     }
@@ -2883,7 +2883,7 @@ static int img_rebase(int argc, char **argv)
      * Ignore the old backing file for unsafe rebase in case we want to correct
      * the reference to a renamed or moved backing file.
      */
-    blk = img_open(image_opts, filename, fmt, flags, true, quiet);
+    blk = img_open(image_opts, filename, fmt, flags, quiet);
     if (!blk) {
         ret = -1;
         goto out;
@@ -3221,7 +3221,7 @@ static int img_resize(int argc, char **argv)
     qemu_opts_del(param);
 
     blk = img_open(image_opts, filename, fmt,
-                   BDRV_O_FLAGS | BDRV_O_RDWR, true, quiet);
+                   BDRV_O_FLAGS | BDRV_O_RDWR, quiet);
     if (!blk) {
         ret = -1;
         goto out;
@@ -3380,7 +3380,7 @@ static int img_amend(int argc, char **argv)
         goto out;
     }
 
-    blk = img_open(image_opts, filename, fmt, flags, true, quiet);
+    blk = img_open(image_opts, filename, fmt, flags, quiet);
     if (!blk) {
         ret = -1;
         goto out;