Patchwork [v4,16/21] qemu-img: add a "map" subcommand

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Submitter Paolo Bonzini
Date Aug. 29, 2013, 2 p.m.
Message ID <1377784821-29561-17-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/270841/
State New
Headers show

Comments

Paolo Bonzini - Aug. 29, 2013, 2 p.m.
This command dumps the metadata of an entire chain, in either tabular or JSON
format.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 qemu-img-cmds.hx |   6 ++
 qemu-img.c       | 191 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 197 insertions(+)
Eric Blake - Aug. 29, 2013, 10:49 p.m.
On 08/29/2013 08:00 AM, Paolo Bonzini wrote:
> This command dumps the metadata of an entire chain, in either tabular or JSON
> format.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  qemu-img-cmds.hx |   6 ++
>  qemu-img.c       | 191 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 197 insertions(+)
> 

> +++ b/qemu-img-cmds.hx
> @@ -45,6 +45,12 @@ STEXI
>  @item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename}
>  ETEXI
>  
> +DEF("map", img_map,
> +    "map [-f fmt] [--output=ofmt] filename")
> +STEXI
> +@item map [-f @var{fmt}] [--output=@var{ofmt}] @var{filename}
> +ETEXI
> +

Should the matching changes to qemu.texi (currently in 17/21) be hoisted
into this patch?

> +    case OFORMAT_HUMAN:
> +        if ((e->flags & BDRV_BLOCK_DATA) &&
> +            !(e->flags & BDRV_BLOCK_OFFSET_VALID)) {
> +            error_report("File contains external, encrypted or compressed clusters.");
> +            exit(1);
> +        }
> +        if ((e->flags & (BDRV_BLOCK_DATA|BDRV_BLOCK_ZERO)) == BDRV_BLOCK_DATA) {
> +            printf("%#-16"PRIx64"%#-16"PRIx64"%#-16"PRIx64"%s\n",

printf("%#x", 0) prints 0, not 0x0.  The automatic 0x is only for
non-zero values; do we really want 0 to look different in the output
from all other values?  Let's see...

> +                   e->start, e->length, e->offset, e->bs->filename);

e->length is always non-zero.  For a qcow2 file, e->offset will never be
0 (the first raw cluster is always after the metadata).  But for a raw
file, the file starts at 0, so e->offset could be 0 there - is your new
'map' subcommand a useful way to probe where the holes are in a sparse
raw file?  But e->start will cover at most one entry starting at 0 (none
if the logical data is unallocated at the start of the file, since the
human output elides those blocks); and indeed, your example in 17/21
shows the special casing:

+@example
+Offset          Length          Mapped to       File
+0               0x20000         0x50000         /tmp/overlay.qcow2
+0x100000        0x10000         0x95380000      /tmp/backing.qcow2

I would have written "0x%-16"PRIx64 instead of "%#-16"PRIx64, but I can
live with your version.

> +    case OFORMAT_JSON:
> +        printf("%s{ \"start\": %"PRId64", \"length\": %"PRId64", \"depth\": %d,"
> +               " \"zero\": %s, \"data\": %s",
> +               (e->start == 0 ? "[" : ",\n"),

Here, e->start==0 will always be present, even when unallocated (since
you don't elide any blocks, and the logical data always starts at 0).

> +
> +    if (output_format == OFORMAT_HUMAN) {
> +        printf("%-16s%-16s%-16s%s\n", "Offset", "Length", "Mapped to", "File");

Are we ever planning on marking up qemu-img for translation?  But this
patch need not worry about it.

Reviewed-by: Eric Blake <eblake@redhat.com>

Patch

diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 4ca7e95..c97a1f4 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -45,6 +45,12 @@  STEXI
 @item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename}
 ETEXI
 
+DEF("map", img_map,
+    "map [-f fmt] [--output=ofmt] filename")
+STEXI
+@item map [-f @var{fmt}] [--output=@var{ofmt}] @var{filename}
+ETEXI
+
 DEF("snapshot", img_snapshot,
     "snapshot [-q] [-l | -a snapshot | -c snapshot | -d snapshot] filename")
 STEXI
diff --git a/qemu-img.c b/qemu-img.c
index d50e0fc..12d2f6e 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1778,6 +1778,198 @@  static int img_info(int argc, char **argv)
     return 0;
 }
 
+
+typedef struct MapEntry {
+    int flags;
+    int depth;
+    int64_t start;
+    int64_t length;
+    int64_t offset;
+    BlockDriverState *bs;
+} MapEntry;
+
+static void dump_map_entry(OutputFormat output_format, MapEntry *e,
+                           MapEntry *next)
+{
+    switch (output_format) {
+    case OFORMAT_HUMAN:
+        if ((e->flags & BDRV_BLOCK_DATA) &&
+            !(e->flags & BDRV_BLOCK_OFFSET_VALID)) {
+            error_report("File contains external, encrypted or compressed clusters.");
+            exit(1);
+        }
+        if ((e->flags & (BDRV_BLOCK_DATA|BDRV_BLOCK_ZERO)) == BDRV_BLOCK_DATA) {
+            printf("%#-16"PRIx64"%#-16"PRIx64"%#-16"PRIx64"%s\n",
+                   e->start, e->length, e->offset, e->bs->filename);
+        }
+        /* This format ignores the distinction between 0, ZERO and ZERO|DATA.
+         * Modify the flags here to allow more coalescing.
+         */
+        if (next &&
+            (next->flags & (BDRV_BLOCK_DATA|BDRV_BLOCK_ZERO)) != BDRV_BLOCK_DATA) {
+            next->flags &= ~BDRV_BLOCK_DATA;
+            next->flags |= BDRV_BLOCK_ZERO;
+        }
+        break;
+    case OFORMAT_JSON:
+        printf("%s{ \"start\": %"PRId64", \"length\": %"PRId64", \"depth\": %d,"
+               " \"zero\": %s, \"data\": %s",
+               (e->start == 0 ? "[" : ",\n"),
+               e->start, e->length, e->depth,
+               (e->flags & BDRV_BLOCK_ZERO) ? "true" : "false",
+               (e->flags & BDRV_BLOCK_DATA) ? "true" : "false");
+        if (e->flags & BDRV_BLOCK_OFFSET_VALID) {
+            printf(", 'offset': %"PRId64"", e->offset);
+        }
+        putchar('}');
+
+        if (!next) {
+            printf("]\n");
+        }
+        break;
+    }
+}
+
+static int get_block_status(BlockDriverState *bs, int64_t sector_num,
+                            int nb_sectors, MapEntry *e)
+{
+    int64_t ret;
+    int depth;
+
+    /* As an optimization, we could cache the current range of unallocated
+     * clusters in each file of the chain, and avoid querying the same
+     * range repeatedly.
+     */
+
+    depth = 0;
+    for (;;) {
+        ret = bdrv_get_block_status(bs, sector_num, nb_sectors, &nb_sectors);
+        if (ret < 0) {
+            return ret;
+        }
+        assert(nb_sectors);
+        if (ret & (BDRV_BLOCK_ZERO|BDRV_BLOCK_DATA)) {
+            break;
+        }
+        bs = bs->backing_hd;
+        if (bs == NULL) {
+            ret = 0;
+            break;
+        }
+
+        depth++;
+    }
+
+    e->start = sector_num * BDRV_SECTOR_SIZE;
+    e->length = nb_sectors * BDRV_SECTOR_SIZE;
+    e->flags = ret & ~BDRV_BLOCK_OFFSET_MASK;
+    e->offset = ret & BDRV_BLOCK_OFFSET_MASK;
+    e->depth = depth;
+    e->bs = bs;
+    return 0;
+}
+
+static int img_map(int argc, char **argv)
+{
+    int c;
+    OutputFormat output_format = OFORMAT_HUMAN;
+    BlockDriverState *bs;
+    const char *filename, *fmt, *output;
+    int64_t length;
+    MapEntry curr = { .length = 0 }, next;
+    int ret = 0;
+
+    fmt = NULL;
+    output = NULL;
+    for (;;) {
+        int option_index = 0;
+        static const struct option long_options[] = {
+            {"help", no_argument, 0, 'h'},
+            {"format", required_argument, 0, 'f'},
+            {"output", required_argument, 0, OPTION_OUTPUT},
+            {0, 0, 0, 0}
+        };
+        c = getopt_long(argc, argv, "f:h",
+                        long_options, &option_index);
+        if (c == -1) {
+            break;
+        }
+        switch (c) {
+        case '?':
+        case 'h':
+            help();
+            break;
+        case 'f':
+            fmt = optarg;
+            break;
+        case OPTION_OUTPUT:
+            output = optarg;
+            break;
+        }
+    }
+    if (optind >= argc) {
+        help();
+    }
+    filename = argv[optind++];
+
+    if (output && !strcmp(output, "json")) {
+        output_format = OFORMAT_JSON;
+    } else if (output && !strcmp(output, "human")) {
+        output_format = OFORMAT_HUMAN;
+    } else if (output) {
+        error_report("--output must be used with human or json as argument.");
+        return 1;
+    }
+
+    bs = bdrv_new_open(filename, fmt, BDRV_O_FLAGS, true, false);
+    if (!bs) {
+        return 1;
+    }
+
+    if (output_format == OFORMAT_HUMAN) {
+        printf("%-16s%-16s%-16s%s\n", "Offset", "Length", "Mapped to", "File");
+    }
+
+    length = bdrv_getlength(bs);
+    while (curr.start + curr.length < length) {
+        int64_t nsectors_left;
+        int64_t sector_num;
+        int n;
+
+        sector_num = (curr.start + curr.length) >> BDRV_SECTOR_BITS;
+
+        /* Probe up to 1 GiB at a time.  */
+        nsectors_left = DIV_ROUND_UP(length, BDRV_SECTOR_SIZE) - sector_num;
+        n = MIN(1 << (30 - BDRV_SECTOR_BITS), nsectors_left);
+        ret = get_block_status(bs, sector_num, n, &next);
+
+        if (ret < 0) {
+            error_report("Could not read file metadata: %s", strerror(-ret));
+            goto out;
+        }
+
+        if (curr.length != 0 && curr.flags == next.flags &&
+            curr.depth == next.depth &&
+            ((curr.flags & BDRV_BLOCK_OFFSET_VALID) == 0 ||
+             curr.offset + curr.length == next.offset)) {
+            curr.length += next.length;
+            continue;
+        }
+
+        if (curr.length > 0) {
+            dump_map_entry(output_format, &curr, &next);
+        }
+        curr = next;
+    }
+
+    dump_map_entry(output_format, &curr, NULL);
+
+out:
+    bdrv_close(bs);
+    bdrv_delete(bs);
+    return ret < 0;
+}
+
 #define SNAPSHOT_LIST   1
 #define SNAPSHOT_CREATE 2
 #define SNAPSHOT_APPLY  3