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>

1 files changed, 62 insertions, 16 deletions

diff --git a/qemu-img.c b/qemu-img.c
index 18caa4b450..df854059be 100644
--- a/qemu-img.c
+++ b/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));