qemu-img: Allow source cache mode specification

Many qemu-img subcommands only read the source file(s) once. For these
use cases, a full write-back cache is unnecessary and mainly clutters
host cache memory. Though this is generally no concern as cache memory
is freely available and can be scaled by the host OS, it may become a
concern with thin provisioning.

For these cases, it makes sense to allow users to freely specify the
source cache mode (e.g. use no cache at all).

This commit adds a new switch (-T) for the qemu-img subcommands check,
compare, convert and rebase to specify the cache to be used for source
images (the backing file in case of rebase).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

qemu-img-cmds.hx

@@ -10,9 +10,9 @@ STEXI
 ETEXI
 
 DEF("check", img_check,
-    "check [-q] [-f fmt] [--output=ofmt]  [-r [leaks | all]] filename")
+    "check [-q] [-f fmt] [--output=ofmt] [-r [leaks | all]] [-T src_cache] filename")
 STEXI
-@item check [-q] [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] @var{filename}
+@item check [-q] [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] @var{filename}
 ETEXI
 
 DEF("create", img_create,
@@ -28,15 +28,15 @@ STEXI
 ETEXI
 
 DEF("compare", img_compare,
-    "compare [-f fmt] [-F fmt] [-p] [-q] [-s] filename1 filename2")
+    "compare [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] filename1 filename2")
 STEXI
-@item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-q] [-s] @var{filename1} @var{filename2}
+@item compare [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-q] [-s] @var{filename1} @var{filename2}
 ETEXI
 
 DEF("convert", img_convert,
-    "convert [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-O output_fmt] [-o options] [-s snapshot_id_or_name] [-l snapshot_param] [-S sparse_size] filename [filename2 [...]] output_filename")
+    "convert [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-o options] [-s snapshot_id_or_name] [-l snapshot_param] [-S sparse_size] filename [filename2 [...]] output_filename")
 STEXI
-@item convert [-c] [-p] [-q] [-n] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@item convert [-c] [-p] [-q] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
 ETEXI
 
 DEF("info", img_info,
@@ -58,9 +58,9 @@ STEXI
 ETEXI
 
 DEF("rebase", img_rebase,
-    "rebase [-q] [-f fmt] [-t cache] [-p] [-u] -b backing_file [-F backing_fmt] filename")
+    "rebase [-q] [-f fmt] [-t cache] [-T src_cache] [-p] [-u] -b backing_file [-F backing_fmt] filename")
 STEXI
-@item rebase [-q] [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
+@item rebase [-q] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
 ETEXI
 
 DEF("resize", img_resize,

qemu-img.c

@@ -109,6 +109,7 @@ static void QEMU_NORETURN help(void)
            "  'cache' is the cache mode used to write the output disk image, the valid\n"
            "    options are: 'none', 'writeback' (default, except for convert), 'writethrough',\n"
            "    'directsync' and 'unsafe' (default for convert)\n"
+           "  'src_cache' in contrast is the cache mode used to read input disk images\n"
            "  'size' is the disk image size in bytes. Optional suffixes\n"
            "    'k' or 'K' (kilobyte, 1024), 'M' (megabyte, 1024k), 'G' (gigabyte, 1024M),\n"
            "    'T' (terabyte, 1024G), 'P' (petabyte, 1024T) and 'E' (exabyte, 1024P)  are\n"
@@ -591,7 +592,7 @@ static int img_check(int argc, char **argv)
 {
     int c, ret;
     OutputFormat output_format = OFORMAT_HUMAN;
-    const char *filename, *fmt, *output;
+    const char *filename, *fmt, *output, *cache;
     BlockDriverState *bs;
     int fix = 0;
     int flags = BDRV_O_FLAGS | BDRV_O_CHECK;
@@ -600,6 +601,7 @@ static int img_check(int argc, char **argv)
 
     fmt = NULL;
     output = NULL;
+    cache = BDRV_DEFAULT_CACHE;
     for(;;) {
         int option_index = 0;
         static const struct option long_options[] = {
@@ -609,7 +611,7 @@ static int img_check(int argc, char **argv)
             {"output", required_argument, 0, OPTION_OUTPUT},
             {0, 0, 0, 0}
         };
-        c = getopt_long(argc, argv, "f:hr:q",
+        c = getopt_long(argc, argv, "hf:r:T:q",
                         long_options, &option_index);
         if (c == -1) {
             break;
@@ -637,6 +639,9 @@ static int img_check(int argc, char **argv)
         case OPTION_OUTPUT:
             output = optarg;
             break;
+        case 'T':
+            cache = optarg;
+            break;
         case 'q':
             quiet = true;
             break;
@@ -656,6 +661,12 @@ static int img_check(int argc, char **argv)
         return 1;
     }
 
+    ret = bdrv_parse_cache_flags(cache, &flags);
+    if (ret < 0) {
+        error_report("Invalid source cache option: %s", cache);
+        return 1;
+    }
+
     bs = bdrv_new_open("image", filename, fmt, flags, true, quiet);
     if (!bs) {
         return 1;
@@ -948,7 +959,7 @@ static int check_empty_sectors(BlockDriverState *bs, int64_t sect_num,
  */
 static int img_compare(int argc, char **argv)
 {
-    const char *fmt1 = NULL, *fmt2 = NULL, *filename1, *filename2;
+    const char *fmt1 = NULL, *fmt2 = NULL, *cache, *filename1, *filename2;
     BlockDriverState *bs1, *bs2;
     int64_t total_sectors1, total_sectors2;
     uint8_t *buf1 = NULL, *buf2 = NULL;
@@ -956,14 +967,16 @@ static int img_compare(int argc, char **argv)
     int allocated1, allocated2;
     int ret = 0; /* return value - 0 Ident, 1 Different, >1 Error */
     bool progress = false, quiet = false, strict = false;
+    int flags;
     int64_t total_sectors;
     int64_t sector_num = 0;
     int64_t nb_sectors;
     int c, pnum;
     uint64_t progress_base;
 
+    cache = BDRV_DEFAULT_CACHE;
     for (;;) {
-        c = getopt(argc, argv, "hpf:F:sq");
+        c = getopt(argc, argv, "hf:F:T:pqs");
         if (c == -1) {
             break;
         }
@@ -978,6 +991,9 @@ static int img_compare(int argc, char **argv)
         case 'F':
             fmt2 = optarg;
             break;
+        case 'T':
+            cache = optarg;
+            break;
         case 'p':
             progress = true;
             break;
@@ -1002,17 +1018,25 @@ static int img_compare(int argc, char **argv)
     filename1 = argv[optind++];
     filename2 = argv[optind++];
 
+    flags = BDRV_O_FLAGS;
+    ret = bdrv_parse_cache_flags(cache, &flags);
+    if (ret < 0) {
+        error_report("Invalid source cache option: %s", cache);
+        ret = 2;
+        goto out3;
+    }
+
     /* Initialize before goto out */
     qemu_progress_init(progress, 2.0);
 
-    bs1 = bdrv_new_open("image 1", filename1, fmt1, BDRV_O_FLAGS, true, quiet);
+    bs1 = bdrv_new_open("image 1", filename1, fmt1, flags, true, quiet);
     if (!bs1) {
         error_report("Can't open file %s", filename1);
         ret = 2;
         goto out3;
     }
 
-    bs2 = bdrv_new_open("image 2", filename2, fmt2, BDRV_O_FLAGS, true, quiet);
+    bs2 = bdrv_new_open("image 2", filename2, fmt2, flags, true, quiet);
     if (!bs2) {
         error_report("Can't open file %s", filename2);
         ret = 2;
@@ -1191,8 +1215,8 @@ static int img_convert(int argc, char **argv)
 {
     int c, n, n1, bs_n, bs_i, compress, cluster_sectors, skip_create;
     int64_t ret = 0;
-    int progress = 0, flags;
-    const char *fmt, *out_fmt, *cache, *out_baseimg, *out_filename;
+    int progress = 0, flags, src_flags;
+    const char *fmt, *out_fmt, *cache, *src_cache, *out_baseimg, *out_filename;
     BlockDriver *drv, *proto_drv;
     BlockDriverState **bs = NULL, *out_bs = NULL;
     int64_t total_sectors, nb_sectors, sector_num, bs_offset;
@@ -1214,11 +1238,12 @@ static int img_convert(int argc, char **argv)
     fmt = NULL;
     out_fmt = "raw";
     cache = "unsafe";
+    src_cache = BDRV_DEFAULT_CACHE;
     out_baseimg = NULL;
     compress = 0;
     skip_create = 0;
     for(;;) {
-        c = getopt(argc, argv, "f:O:B:s:hce6o:pS:t:qnl:");
+        c = getopt(argc, argv, "hf:O:B:ce6o:s:l:S:pt:T:qn");
         if (c == -1) {
             break;
         }
@@ -1299,6 +1324,9 @@ static int img_convert(int argc, char **argv)
         case 't':
             cache = optarg;
             break;
+        case 'T':
+            src_cache = optarg;
+            break;
         case 'q':
             quiet = true;
             break;
@@ -1335,6 +1363,13 @@ static int img_convert(int argc, char **argv)
         goto out;
     }
 
+    src_flags = BDRV_O_FLAGS;
+    ret = bdrv_parse_cache_flags(src_cache, &src_flags);
+    if (ret < 0) {
+        error_report("Invalid source cache option: %s", src_cache);
+        goto out;
+    }
+
     qemu_progress_print(0, 100);
 
     bs = g_new0(BlockDriverState *, bs_n);
@@ -1344,7 +1379,7 @@ static int img_convert(int argc, char **argv)
     for (bs_i = 0; bs_i < bs_n; bs_i++) {
         char *id = bs_n > 1 ? g_strdup_printf("source %d", bs_i)
                             : g_strdup("source");
-        bs[bs_i] = bdrv_new_open(id, argv[optind + bs_i], fmt, BDRV_O_FLAGS,
+        bs[bs_i] = bdrv_new_open(id, argv[optind + bs_i], fmt, src_flags,
                                  true, quiet);
         g_free(id);
         if (!bs[bs_i]) {
@@ -2291,8 +2326,8 @@ static int img_rebase(int argc, char **argv)
     BlockDriverState *bs, *bs_old_backing = NULL, *bs_new_backing = NULL;
     BlockDriver *old_backing_drv, *new_backing_drv;
     char *filename;
-    const char *fmt, *cache, *out_basefmt, *out_baseimg;
-    int c, flags, ret;
+    const char *fmt, *cache, *src_cache, *out_basefmt, *out_baseimg;
+    int c, flags, src_flags, ret;
     int unsafe = 0;
     int progress = 0;
     bool quiet = false;
@@ -2301,10 +2336,11 @@ static int img_rebase(int argc, char **argv)
     /* Parse commandline parameters */
     fmt = NULL;
     cache = BDRV_DEFAULT_CACHE;
+    src_cache = BDRV_DEFAULT_CACHE;
     out_baseimg = NULL;
     out_basefmt = NULL;
     for(;;) {
-        c = getopt(argc, argv, "uhf:F:b:pt:q");
+        c = getopt(argc, argv, "hf:F:b:upt:T:q");
         if (c == -1) {
             break;
         }
@@ -2331,6 +2367,9 @@ static int img_rebase(int argc, char **argv)
         case 't':
             cache = optarg;
             break;
+        case 'T':
+            src_cache = optarg;
+            break;
         case 'q':
             quiet = true;
             break;
@@ -2359,6 +2398,13 @@ static int img_rebase(int argc, char **argv)
         return -1;
     }
 
+    src_flags = BDRV_O_FLAGS;
+    ret = bdrv_parse_cache_flags(src_cache, &src_flags);
+    if (ret < 0) {
+        error_report("Invalid source cache option: %s", src_cache);
+        return -1;
+    }
+
     /*
      * Open the images.
      *
@@ -2402,7 +2448,7 @@ static int img_rebase(int argc, char **argv)
 
         bs_old_backing = bdrv_new("old_backing", &error_abort);
         bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
-        ret = bdrv_open(&bs_old_backing, backing_name, NULL, NULL, BDRV_O_FLAGS,
+        ret = bdrv_open(&bs_old_backing, backing_name, NULL, NULL, src_flags,
                         old_backing_drv, &local_err);
         if (ret) {
             error_report("Could not open old backing file '%s': %s",
@@ -2412,8 +2458,8 @@ static int img_rebase(int argc, char **argv)
         }
         if (out_baseimg[0]) {
             bs_new_backing = bdrv_new("new_backing", &error_abort);
-            ret = bdrv_open(&bs_new_backing, out_baseimg, NULL, NULL,
-                            BDRV_O_FLAGS, new_backing_drv, &local_err);
+            ret = bdrv_open(&bs_new_backing, out_baseimg, NULL, NULL, src_flags,
+                            new_backing_drv, &local_err);
             if (ret) {
                 error_report("Could not open new backing file '%s': %s",
                              out_baseimg, error_get_pretty(local_err));

qemu-img.texi

@@ -72,6 +72,9 @@ down to the nearest 512 bytes. You may use the common size suffixes like
 specifies the cache mode that should be used with the (destination) file. See
 the documentation of the emulator's @code{-drive cache=...} option for allowed
 values.
+@item -T @var{src_cache}
+in contrast specifies the cache mode that should be used with the source
+file(s).
 @end table
 
 Parameters to snapshot subcommand:
@@ -113,7 +116,7 @@ Skip the creation of the target volume
 Command description:
 
 @table @option
-@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] @var{filename}
+@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] @var{filename}
 
 Perform a consistency check on the disk image @var{filename}. The command can
 output in the format @var{ofmt} which is either @code{human} or @code{json}.
@@ -172,7 +175,7 @@ the backing file, the backing file will not be truncated.  If you want the
 backing file to match the size of the smaller snapshot, you can safely truncate
 it yourself once the commit operation successfully completes.
 
-@item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2}
+@item compare [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-s] [-q] @var{filename1} @var{filename2}
 
 Check if two images have the same content. You can compare images with
 different format or settings.
@@ -213,7 +216,7 @@ Error on reading data
 
 @end table
 
-@item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
 
 Convert the disk image @var{filename} or a snapshot @var{snapshot_param}(@var{snapshot_id_or_name} is deprecated)
 to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}
@@ -325,7 +328,7 @@ source code.
 
 List, apply, create or delete snapshots in image @var{filename}.
 
-@item rebase [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
+@item rebase [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
 
 Changes the backing file of an image. Only the formats @code{qcow2} and
 @code{qed} support changing the backing file.
@@ -336,6 +339,9 @@ The backing file is changed to @var{backing_file} and (if the image format of
 string), then the image is rebased onto no backing file (i.e. it will exist
 independently of any backing file).
 
+@var{cache} specifies the cache mode to be used for @var{filename}, whereas
+@var{src_cache} specifies the cache mode for reading the new backing file.
+
 There are two different modes in which @code{rebase} can operate:
 @table @option
 @item Safe mode