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[int13] Do not report INT 13 extension support for emulated floppies 

The INT 13 extensions provide a mechanism for accessing disks using
linear (LBA) rather than C/H/S addressing.  SAN protocols such as
iSCSI invariably support only linear addresses and so iPXE currently
provides LBA access to all SAN disks (with autodetection and emulation
of an appropriate geometry for C/H/S accesses).

Most BIOSes will not report support for INT 13 extensions for floppy
disk drives, and some operating systems may be confused by a floppy
drive that claims such support.

Minimise surprise by reporting the existence of support for INT 13
extensions only for non-floppy drive numbers.  Continue to provide
support for all drive numbers, to avoid breaking operating systems
that may unconditionally use the INT 13 extensions without first
checking for support.

Reported-by: Valdo Toost <vtoost@hot.ee>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
pull/329/head
Michael Brown 2021-04-13 20:30:20 +01:00
parent 3ae83222ce
commit 8ca43ccbc1
1 changed files with 2 additions and 2 deletions
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4
src/arch/x86/interface/pcbios/int13.c
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@ -678,10 +678,10 @@ static int int13_get_disk_type ( struct san_device *sandev,
* @ret cx Extensions API support bitmap
* @ret status Status code / API version
*/
static int int13_extension_check ( struct san_device *sandev __unused,
static int int13_extension_check ( struct san_device *sandev,
struct i386_all_regs *ix86 ) {
if ( ix86->regs.bx == 0x55aa ) {
if ( ( ix86->regs.bx == 0x55aa ) && ! int13_is_fdd ( sandev ) ) {
DBGC2 ( sandev, "INT13 extensions installation check\n" );
ix86->regs.bx = 0xaa55;
ix86->regs.cx = ( INT13_EXTENSION_LINEAR |