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

[Paolo Bonzini]

Il 30/07/2013 17:13, Kevin Wolf ha scritto:
> 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 <address@hidden>
> 
> 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?

I would remove the one in qemu-io (but I haven't checked if qemu-iotests
uses it).

>> 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?

I will change it to use tabs and add a heading line.

>> +        }
>> +        /* 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.

Will fix.

>> +        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.

Good idea.  I'll make this change in a separate patch.

>> +        }
>> +
>> +        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.

I'll make it always use bs->total_sectors instead of fixing this.

>> +    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.

Right.

Paolo

>> +        }
>> +
>> +        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
> 
>