Re: [Qemu-devel] [PATCH v3 13/19] qemu-img: add a "map" subcommand

[Kevin Wolf <kwolf@redhat.com>]

Am 25.07.2013 um 16:23 hat Paolo Bonzini geschrieben:
> This command dumps the metadata of an entire chain, in either tabular or JSON
> format.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Hm, we have a 'map' command in qemu-io, which isn't exactly the same,
but then not much different either.

Depending on the use cases, should we move this to qemu-io, should we
remove the old function from qemu-io, or should we really keep both?

> diff --git a/qemu-img.c b/qemu-img.c
> index c5c8ebc..b28d388 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1768,6 +1768,192 @@ 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;
> +} 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("%"PRId64" %"PRId64" %d %"PRId64"\n",
> +                   e->start, e->length, e->depth, e->offset);

Is this really human-readable output?

> +        }
> +        /* 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");

Correct JSON uses double quotes.

> +        if (e->flags & BDRV_BLOCK_OFFSET_VALID) {
> +            printf(", 'offset': %"PRId64"", e->offset);
> +        }
> +        putchar('}');
> +
> +        if (!next) {
> +            printf("]\n");
> +        }
> +        break;
> +    }
> +}
> +
> +static int64_t get_block_status(BlockDriverState *bs, int64_t sector_num,
> +                                int *nb_sectors, int *depth)
> +{
> +    int64_t ret;
> +
> +    /* 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 (;;) {
> +        int orig_nb_sectors = *nb_sectors;
> +
> +        ret = bdrv_get_block_status(bs, sector_num, *nb_sectors, nb_sectors);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +        if (ret & (BDRV_BLOCK_ZERO|BDRV_BLOCK_DATA)) {
> +            return ret;
> +        }
> +        if (!*nb_sectors) {
> +            /* Beyond the end of this image.  The extra data is read as zeroes.
> +             * We're in the range of the BlockDriverState above this one, so
> +             * adjust depth.
> +             */
> +            *nb_sectors = orig_nb_sectors;
> +            (*depth)--;
> +            return BDRV_BLOCK_ZERO;

If you implement my suggestion that bdrv_co_get_block_status() returns
BDRV_BLOCK_ZERO instead of 0 if the image has no backing file, it might
also make sense to put this check there and return BDRV_BLOCK_ZERO even
if it has a backing file, but we're after its end.

> +        }
> +
> +        bs = bs->backing_hd;
> +        if (bs == NULL) {
> +            return 0;
> +        }
> +
> +        (*depth)++;
> +    }
> +}
> +
> +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;
> +
> +    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;
> +    }
> +
> +    length = bdrv_getlength(bs);

bdrv_getlength() can fail.

> +    while (curr.start + curr.length < length) {
> +        int64_t nsectors_left, ret;
> +        int64_t sector_num;
> +        int n, depth, flags;
> +
> +        /* Probe up to 1 G at a time.  */
> +        sector_num = (curr.start + curr.length) >> BDRV_SECTOR_BITS;
> +        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, &depth);
> +
> +        if (ret < 0) {
> +            error_report("Could not read file metadata: %s", strerror(-ret));
> +            return 1;

This leaks bs.

> +        }
> +
> +        flags = ret & ~BDRV_BLOCK_OFFSET_MASK;
> +        ret &= BDRV_BLOCK_OFFSET_MASK;
> +        if (curr.length == 0 || curr.flags != flags || curr.depth != depth ||
> +            ((curr.flags & BDRV_BLOCK_OFFSET_VALID) &&
> +             curr.offset + curr.length != ret)) {
> +            next.flags = flags;
> +            next.depth = depth;
> +            next.start = sector_num << BDRV_SECTOR_BITS;
> +            next.offset = ret;
> +            next.length = 0;
> +            if (curr.length > 0) {
> +                dump_map_entry(output_format, &curr, &next);
> +            }
> +            curr = next;
> +        }
> +        curr.length += n << BDRV_SECTOR_BITS;
> +    }
> +
> +    dump_map_entry(output_format, &curr, NULL);
> +    return 0;
> +}
> +
>  #define SNAPSHOT_LIST   1
>  #define SNAPSHOT_CREATE 2
>  #define SNAPSHOT_APPLY  3

Kevin