From 422865f6672ee1482b98d18321b55c1ecfb06c82 Mon Sep 17 00:00:00 2001 From: Thomas Huth Date: Mon, 4 Jul 2022 13:18:54 +0200 Subject: pc-bios/s390-ccw/bootmap: Improve the guessing logic in zipl_load_vblk() The logic of trying an final ISO or ECKD boot on virtio-block devices is very weird: Since the geometry hardly ever matches in virtio_disk_is_scsi(), virtio_blk_setup_device() always sets a "guessed" disk geometry via virtio_assume_scsi() (which is certainly also wrong in a lot of cases). zipl_load_vblk() then sees that there's been a "virtio_guessed_disk_nature" and tries to fix up the geometry again via virtio_assume_iso9660() before always trying to do ipl_iso_el_torito(). That's a very brain-twisting way of attempting to boot from ISO images, which won't work anymore after the following patches that will clean up the virtio_assume_scsi() mess (and thus get rid of the "virtio_guessed_disk_nature" here). Let's try a better approach instead: ISO files always have a magic string "CD001" at offset 0x8001 (see e.g. the ECMA-119 specification) which we can use to decide whether we should try to boot in ISO 9660 mode (which we should also try if we see a sector size of 2048). And if we were not able to boot in ISO mode here, the final boot attempt before panicking is to boot in ECKD mode. Since this is our last boot attempt anyway, simply always assume the ECKD geometry here (if the sector size was not 4096 yet), so that we also do not depend on the guessed disk geometry from virtio_blk_setup_device() here anymore. Message-Id: <20220704111903.62400-4-thuth@redhat.com> Signed-off-by: Thomas Huth --- pc-bios/s390-ccw/bootmap.c | 27 +++++++++++++++++++++++---- 1 file changed, 23 insertions(+), 4 deletions(-) diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c index 56411ab..994e59c 100644 --- a/pc-bios/s390-ccw/bootmap.c +++ b/pc-bios/s390-ccw/bootmap.c @@ -780,18 +780,37 @@ static void ipl_iso_el_torito(void) } } +/** + * Detect whether we're trying to boot from an .ISO image. + * These always have a signature string "CD001" at offset 0x8001. + */ +static bool has_iso_signature(void) +{ + int blksize = virtio_get_block_size(); + + if (!blksize || virtio_read(0x8000 / blksize, sec)) { + return false; + } + + return !memcmp("CD001", &sec[1], 5); +} + /*********************************************************************** * Bus specific IPL sequences */ static void zipl_load_vblk(void) { - if (virtio_guessed_disk_nature()) { - virtio_assume_iso9660(); + int blksize = virtio_get_block_size(); + + if (blksize == VIRTIO_ISO_BLOCK_SIZE || has_iso_signature()) { + if (blksize != VIRTIO_ISO_BLOCK_SIZE) { + virtio_assume_iso9660(); + } + ipl_iso_el_torito(); } - ipl_iso_el_torito(); - if (virtio_guessed_disk_nature()) { + if (blksize != VIRTIO_DASD_DEFAULT_BLOCK_SIZE) { sclp_print("Using guessed DASD geometry.\n"); virtio_assume_eckd(); } -- cgit v1.1