dos: always try the FAT32-aware direct I/O calls first

Always try the FAT32-aware direct I/O calls before trying the legacy
raw I/O calls.  The reason for doing this is that the FAT32 stuff may
be implemented as an add-on.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/dos/syslinux.c b/dos/syslinux.c
index d054c4c..ca2fd8e 100644 (file)
--- a/dos/syslinux.c
+++ b/dos/syslinux.c
@@ -171,13 +171,15 @@ void write_device(int drive, const void *buf, size_t nsecs, unsigned int sector)
     dio.bufoffs = (uintptr_t) buf;
     dio.bufseg = data_segment();
 
-    if (dos_version >= 0x070a) {
-       asm volatile("int $0x21 ; setc %0"
-                    : "=bcdm" (err), "=a" (errnum)
-                    : "a" (0x7305), "b" (&dio), "c" (-1), "d" (drive),
-                      "S" (1), "m" (dio)
-                    : "memory");
-    } else {
+    /* Try FAT32-aware system call first */
+    asm volatile("int $0x21 ; setc %0"
+                : "=bcdm" (err), "=a" (errnum)
+                : "a" (0x7305), "b" (&dio), "c" (-1), "d" (drive),
+                  "S" (1), "m" (dio)
+                : "memory");
+
+    if (err && errnum == 0x0001) {
+       /* Try legacy system call */
        asm volatile("int $0x26 ; setc %0 ; popfw"
                     : "=bcdm" (err), "=a" (errnum)
                     : "a" (drive-1), "b" (&dio), "c" (-1), "d" (buf),
@@ -204,12 +206,14 @@ void read_device(int drive, const void *buf, size_t nsecs, unsigned int sector)
     dio.bufoffs = (uintptr_t) buf;
     dio.bufseg = data_segment();
 
-    if (dos_version >= 0x070a) {
-       asm volatile("int $0x21 ; setc %0"
-                    : "=bcdm" (err), "=a" (errnum)
-                    : "a" (0x7305), "b" (&dio), "c" (-1), "d" (drive),
-                    "S" (0), "m" (dio));
-    } else {
+    /* Try FAT32-aware system call first */
+    asm volatile("int $0x21 ; setc %0"
+                : "=bcdm" (err), "=a" (errnum)
+                : "a" (0x7305), "b" (&dio), "c" (-1), "d" (drive),
+                  "S" (0), "m" (dio));
+
+    if (err && errnum == 0x0001) {
+       /* Try legacy system call */
        asm volatile("int $0x25 ; setc %0 ; popfw"
                     : "=bcdm" (err), "=a" (errnum)
                     : "a" (drive-1), "b" (&dio), "c" (-1), "d" (buf),