[Qemu-devel] [PATCH v3 1/1] atapi: abort transfers with 0 byte limits

[John Snow <jsnow@redhat.com>]

We're supposed to abort on transfers like this, unless we fill
Word 125 of our IDENTIFY data with a default transfer size, which
we don't currently do.

This is an ATA error, not a SCSI/ATAPI one.
See ATA8-ACS3 sections 7.17.6.49 or 7.21.5.

If we don't do this, QEMU will loop forever trying to transfer
zero bytes, which isn't particularly useful.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 hw/ide/atapi.c    | 32 +++++++++++++++++++++++++++-----
 hw/ide/core.c     |  2 +-
 hw/ide/internal.h |  1 +
 3 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/hw/ide/atapi.c b/hw/ide/atapi.c
index 79dd167..747f466 100644
--- a/hw/ide/atapi.c
+++ b/hw/ide/atapi.c
@@ -1169,20 +1169,28 @@ enum {
      * 4.1.8)
      */
     CHECK_READY = 0x02,
+
+    /*
+     * Commands flagged with NONDATA do not in any circumstances return
+     * any data via ide_atapi_cmd_reply. These commands are exempt from
+     * the normal byte_count_limit constraints.
+     * See ATA8-ACS3 "7.21.5 Byte Count Limit"
+     */
+    NONDATA = 0x04,
 };
 
 static const struct {
     void (*handler)(IDEState *s, uint8_t *buf);
     int flags;
 } atapi_cmd_table[0x100] = {
-    [ 0x00 ] = { cmd_test_unit_ready,               CHECK_READY },
+    [ 0x00 ] = { cmd_test_unit_ready,               CHECK_READY | NONDATA },
     [ 0x03 ] = { cmd_request_sense,                 ALLOW_UA },
     [ 0x12 ] = { cmd_inquiry,                       ALLOW_UA },
-    [ 0x1b ] = { cmd_start_stop_unit,               0 }, /* [1] */
-    [ 0x1e ] = { cmd_prevent_allow_medium_removal,  0 },
+    [ 0x1b ] = { cmd_start_stop_unit,               NONDATA }, /* [1] */
+    [ 0x1e ] = { cmd_prevent_allow_medium_removal,  NONDATA },
     [ 0x25 ] = { cmd_read_cdvd_capacity,            CHECK_READY },
     [ 0x28 ] = { cmd_read, /* (10) */               CHECK_READY },
-    [ 0x2b ] = { cmd_seek,                          CHECK_READY },
+    [ 0x2b ] = { cmd_seek,                          CHECK_READY | NONDATA },
     [ 0x43 ] = { cmd_read_toc_pma_atip,             CHECK_READY },
     [ 0x46 ] = { cmd_get_configuration,             ALLOW_UA },
     [ 0x4a ] = { cmd_get_event_status_notification, ALLOW_UA },
@@ -1190,7 +1198,7 @@ static const struct {
     [ 0x5a ] = { cmd_mode_sense, /* (10) */         0 },
     [ 0xa8 ] = { cmd_read, /* (12) */               CHECK_READY },
     [ 0xad ] = { cmd_read_dvd_structure,            CHECK_READY },
-    [ 0xbb ] = { cmd_set_speed,                     0 },
+    [ 0xbb ] = { cmd_set_speed,                     NONDATA },
     [ 0xbd ] = { cmd_mechanism_status,              0 },
     [ 0xbe ] = { cmd_read_cd,                       CHECK_READY },
     /* [1] handler detects and reports not ready condition itself */
@@ -1251,6 +1259,20 @@ void ide_atapi_cmd(IDEState *s)
         return;
     }
 
+    /* Nondata commands permit the byte_count_limit to be 0.
+     * If this is a data-transferring PIO command and BCL is 0,
+     * we abort at the /ATA/ level, not the ATAPI level.
+     * See ATA8 ACS3 section 7.17.6.49 and 7.21.5 */
+    if (!(atapi_cmd_table[s->io_buffer[0]].flags & NONDATA)) {
+        /* TODO: Check IDENTIFY data word 125 for default BCL (currently 0) */
+        uint16_t byte_count_limit = s->lcyl | (s->hcyl << 8);
+        if (!(byte_count_limit || s->atapi_dma)) {
+            /* TODO: Move abort back into core.c and make static inline again */
+            ide_abort_command(s);
+            return;
+        }
+    }
+
     /* Execute the command */
     if (atapi_cmd_table[s->io_buffer[0]].handler) {
         atapi_cmd_table[s->io_buffer[0]].handler(s, buf);
diff --git a/hw/ide/core.c b/hw/ide/core.c
index 50449ca..28cf535 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -457,7 +457,7 @@ BlockAIOCB *ide_issue_trim(BlockBackend *blk,
     return &iocb->common;
 }
 
-static inline void ide_abort_command(IDEState *s)
+void ide_abort_command(IDEState *s)
 {
     ide_transfer_stop(s);
     s->status = READY_STAT | ERR_STAT;
diff --git a/hw/ide/internal.h b/hw/ide/internal.h
index 30fdcbc..40e1aa4 100644
--- a/hw/ide/internal.h
+++ b/hw/ide/internal.h
@@ -537,6 +537,7 @@ void ide_set_sector(IDEState *s, int64_t sector_num);
 
 void ide_start_dma(IDEState *s, BlockCompletionFunc *cb);
 void ide_dma_error(IDEState *s);
+void ide_abort_command(IDEState *s);
 
 void ide_atapi_cmd_ok(IDEState *s);
 void ide_atapi_cmd_error(IDEState *s, int sense_key, int asc);
-- 
2.4.3