block/dmg: properly detect the UDIF trailer
DMG files have a variable length with a UDIF trailer at the end of a file. This UDIF trailer is essential as it describes the contents of the image. At the moment however, the start of this trailer is almost always incorrect as bdrv_getlength() returns a multiple of the block size (rounded up). This results in a failure to recognize DMG files, resulting in Invalid argument (EINVAL) errors. As there is no API to retrieve the real file size, look for the magic header in the last two sectors to find the start of this 512-byte UDIF trailer (the "koly" block). The resource fork offset ("info_begin") has its offset adjusted as the initial value of offset does not mean "end of file" anymore, but "begin of UDIF trailer". [Replaced error_set(errp, ERROR_CLASS_GENERIC_ERROR, ...) with error_setg(errp, ...) as discussed with Peter. --Stefan] Signed-off-by: NPeter Wu <peter@lekensteyn.nl> Reviewed-by: NJohn Snow <jsnow@redhat.com> Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com> Message-id: 1420566495-13284-2-git-send-email-peter@lekensteyn.nl Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com> Signed-off-by: NKevin Wolf <kwolf@redhat.com>
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