libata: clear dev->ering in smarter way

dev->ering used to be cleared together with the rest of ata_device in
ata_dev_init() which is called whenever a probing event occurs.
dev->ering is about to be used to track probing failures so it needs
to remain persistent over multiple porbing events.  This patch
achieves this by doing the following.

* Instead of CLEAR_OFFSET, define CLEAR_BEGIN and CLEAR_END and only
  clear between BEGIN and END.  ering is moved after END.  The split
  of persistent area is to allow hotter items remain at the head.

* ering is explicitly cleared on ata_dev_disable() and when device
  attach succeeds.  So, ering is persistent throug a device's life
  time (unless explicitly cleared of course) and also through periods
  inbetween disablement of an attached device and successful detection
  of the next one.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 10 insertions, 8 deletions

diff --git a/include/linux/libata.h b/include/linux/libata.h
index bca3ba25f52a..9dcefee5843c 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -580,7 +580,7 @@ struct ata_device {
         acpi_handle             acpi_handle;
         union acpi_object       *gtf_cache;
 #endif
-        /* n_sector is used as CLEAR_OFFSET, read comment above CLEAR_OFFSET */
+        /* n_sector is CLEAR_BEGIN, read comment above CLEAR_BEGIN */
         u64                     n_sectors;      /* size of device, if ATA */
         unsigned int            class;          /* ATA_DEV_xxx */
         unsigned long           unpark_deadline;
@@ -605,20 +605,22 @@ struct ata_device {
         u16                     heads;          /* Number of heads */
         u16                     sectors;        /* Number of sectors per track */
 
-        /* error history */
-        int                     spdn_cnt;
-        struct ata_ering        ering;
-
         union {
                 u16             id[ATA_ID_WORDS]; /* IDENTIFY xxx DEVICE data */
                 u32             gscr[SATA_PMP_GSCR_DWORDS]; /* PMP GSCR block */
         };
+
+        /* error history */
+        int                     spdn_cnt;
+        /* ering is CLEAR_END, read comment above CLEAR_END */
+        struct ata_ering        ering;
 };
 
-/* Offset into struct ata_device.  Fields above it are maintained
- * acress device init.  Fields below are zeroed.
+/* Fields between ATA_DEVICE_CLEAR_BEGIN and ATA_DEVICE_CLEAR_END are
+ * cleared to zero on ata_dev_init().
  */
-#define ATA_DEVICE_CLEAR_OFFSET         offsetof(struct ata_device, n_sectors)
+#define ATA_DEVICE_CLEAR_BEGIN          offsetof(struct ata_device, n_sectors)
+#define ATA_DEVICE_CLEAR_END            offsetof(struct ata_device, ering)
 
 struct ata_eh_info {
         struct ata_device       *dev;           /* offending device */