Commit e1c7f0e3 authored by Kevin Wolf's avatar Kevin Wolf Committed by Anthony Liguori
Browse files

qcow2: Store exact backing format length 



Currently qcow2 unnecessarily rounds up the length of the backing format string
to the next multiple of 8. At the same time, the array in BlockDriverState can
only hold 15 characters, so in effect backing formats with 9 characters or more
don't work (e.g. host_device).

Save the real string length and things start to work for all valid image format
names.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
parent f35d68f0

block/qcow2.c

+9 −7
Original line number Diff line number Diff line
@@ -124,12 +124,12 @@ static int qcow_read_extensions(BlockDriverState *bs, uint64_t start_offset, 
#ifdef DEBUG_EXT

            printf("Qcow2: Got format extension %s\n", bs->backing_format);

#endif

            offset += ((ext.len + 7) & ~7);

            offset = ((offset + ext.len + 7) & ~7);

            break;



        default:

            /* unknown magic -- just skip it */

            offset += ((ext.len + 7) & ~7);

            offset = ((offset + ext.len + 7) & ~7);

            break;

        }

    }
@@ -738,6 +738,7 @@ static int qcow_create2(const char *filename, int64_t total_size, 


    int fd, header_size, backing_filename_len, l1_size, i, shift, l2_bits;

    int ref_clusters, backing_format_len = 0;

    int rounded_ext_bf_len = 0;

    QCowHeader header;

    uint64_t tmp, offset;

    QCowCreateState s1, *s = &s1;
@@ -759,8 +760,9 @@ static int qcow_create2(const char *filename, int64_t total_size, 
        if (backing_format) {

            ext_bf.magic = QCOW_EXT_MAGIC_BACKING_FORMAT;

            backing_format_len = strlen(backing_format);

            ext_bf.len = (backing_format_len + 7) & ~7;

            header_size += ((sizeof(ext_bf) + ext_bf.len + 7) & ~7);

            ext_bf.len = backing_format_len;

            rounded_ext_bf_len = (sizeof(ext_bf) + ext_bf.len + 7) & ~7;

            header_size += rounded_ext_bf_len;

        }

        header.backing_file_offset = cpu_to_be64(header_size);

        backing_filename_len = strlen(backing_file);
@@ -828,15 +830,15 @@ static int qcow_create2(const char *filename, int64_t total_size, 
    if (backing_file) {

        if (backing_format_len) {

            char zero[16];

            int d = ext_bf.len - backing_format_len;

            int padding = rounded_ext_bf_len - (ext_bf.len + sizeof(ext_bf));



            memset(zero, 0, sizeof(zero));

            cpu_to_be32s(&ext_bf.magic);

            cpu_to_be32s(&ext_bf.len);

            write(fd, &ext_bf, sizeof(ext_bf));

            write(fd, backing_format, backing_format_len);

            if (d>0) {

                write(fd, zero, d);

            if (padding > 0) {

                write(fd, zero, padding);

            }

        }

        write(fd, backing_file, backing_filename_len);