[PATCH 1/2] cdrom: Break up very large read requests into smaller requests

[Kevin O'Connor]

A cdrom boot image could be over 64K in size, but the low level
drivers may not support very large reads.  If a large cdrom image is
found, issue multiple reads so that a read request over 64K is never
issued.

Signed-off-by: Kevin O'Connor 
---
 src/cdrom.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/cdrom.c b/src/cdrom.c
index de0e7de..92f34f4 100644
--- a/src/cdrom.c
+++ b/src/cdrom.c
@@ -212,12 +212,21 @@ cdrom_boot(struct drive_s *drive)
     CDEmu.device_spec = drive->cntl_id % 2;

// And we read the image in memory
+    nbsectors = DIV_ROUND_UP(nbsectors, 4);
     dop.lba = lba;
-    dop.count = DIV_ROUND_UP(nbsectors, 4);
     dop.buf_fl = MAKE_FLATPTR(boot_segment, 0);
-    ret = scsi_process_op(&dop);
-    if (ret)
-        return 12;
+    while (nbsectors) {
+        int count = nbsectors;
+        if (count > 64*1024/CDROM_SECTOR_SIZE)
+            count = 64*1024/CDROM_SECTOR_SIZE;
+        dop.count = count;
+        ret = scsi_process_op(&dop);
+        if (ret)
+            return 12;
+        nbsectors -= count;
+        dop.lba += count;
+        dop.buf_fl += count*CDROM_SECTOR_SIZE;
+    }

if (media == 0) {
         // No emulation requested - return success.

[PATCH 2/2] block: Check for read/write requests over 64K

[Kevin O'Connor]

The standard BIOS disk read/write request interface should never get a
request for more than 64K of data.  Explicitly check for overly large
requests and reject them.  This way, the low-level drivers do not need
to check for or attempt to handle very large requests.

Signed-off-by: Kevin O'Connor 
---
 src/block.c | 4 ++++
 src/disk.c  | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/src/block.c b/src/block.c
index 43af305..3f7ecb1 100644
--- a/src/block.c
+++ b/src/block.c
@@ -485,6 +485,10 @@ process_op(struct disk_op_s *op)
 {
     ASSERT16();
     int ret, origcount = op->count;
+    if (origcount * GET_GLOBALFLAT(op->drive_gf->blksize) > 64*1024) {
+        op->count = 0;
+        return DISK_RET_EBOUNDARY;
+    }
     u8 type = GET_GLOBALFLAT(op->drive_gf->type);
     switch (type) {
     case DTYPE_FLOPPY:
diff --git a/src/disk.c b/src/disk.c
index fe2e2c3..0e0af24 100644
--- a/src/disk.c
+++ b/src/disk.c
@@ -173,6 +173,7 @@ disk_1300(struct bregs *regs, struct drive_s *drive_gf)
     struct disk_op_s dop;
     dop.drive_gf = drive_gf;
     dop.command = CMD_RESET;
+    dop.count = 0;
     int status = send_disk_op(&dop);
     disk_ret(regs, status);
 }
@@ -322,6 +323,7 @@ disk_1310(struct bregs *regs, struct drive_s *drive_gf)
     struct disk_op_s dop;
     dop.drive_gf = drive_gf;
     dop.command = CMD_ISREADY;
+    dop.count = 0;
     int status = send_disk_op(&dop);
     disk_ret(regs, status);
 }