ore: Support for short read/writes

Memory conditions and max_bio constraints might cause us to
not comply to the full length of the requested IO. Instead of
failing the complete IO we can issue a shorter read/write and
report how much was actually executed in the ios->length
member.

All users must check ios->length at IO_done or upon return of
ore_read/write and re-issue the reminder of the bytes. Because
other wise there is no error returned like before.

This is part of the effort to support the pnfs-obj layout driver.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

1 files changed, 23 insertions, 7 deletions

diff --git a/fs/exofs/ore.c b/fs/exofs/ore.c
index d0f8db5e46c5..8354fe061d1c 100644
--- a/fs/exofs/ore.c
+++ b/fs/exofs/ore.c
@@ -377,8 +377,8 @@ static int _add_stripe_unit(struct ore_io_state *ios,  unsigned *cur_pg,
         unsigned pg = *cur_pg;
         struct request_queue *q =
                         osd_request_queue(_ios_od(ios, per_dev->dev));
-
-        per_dev->length += cur_len;
+        unsigned len = cur_len;
+        int ret;
 
         if (per_dev->bio == NULL) {
                 unsigned pages_in_stripe = ios->layout->group_width *
@@ -390,7 +390,8 @@ static int _add_stripe_unit(struct ore_io_state *ios,  unsigned *cur_pg,
                 if (unlikely(!per_dev->bio)) {
                         ORE_DBGMSG("Failed to allocate BIO size=%u\n",
                                      bio_size);
-                        return -ENOMEM;
+                        ret = -ENOMEM;
+                        goto out;
                 }
         }
 
@@ -403,15 +404,24 @@ static int _add_stripe_unit(struct ore_io_state *ios,  unsigned *cur_pg,
 
                 added_len = bio_add_pc_page(q, per_dev->bio, ios->pages[pg],
                                             pglen, pgbase);
-                if (unlikely(pglen != added_len))
-                        return -ENOMEM;
+                if (unlikely(pglen != added_len)) {
+                        ret = -ENOMEM;
+                        goto out;
+                }
                 pgbase = 0;
                 ++pg;
         }
         BUG_ON(cur_len);
 
+        per_dev->length += len;
         *cur_pg = pg;
-        return 0;
+        ret = 0;
+out:    /* we fail the complete unit on an error eg don't advance
+         * per_dev->length and cur_pg. This means that we might have a bigger
+         * bio than the CDB requested length (per_dev->length). That's fine
+         * only the oposite is fatal.
+         */
+        return ret;
 }
 
 static int _prepare_for_striping(struct ore_io_state *ios)
@@ -472,7 +482,13 @@ static int _prepare_for_striping(struct ore_io_state *ios)
 out:
         ios->numdevs = devs_in_group;
         ios->pages_consumed = cur_pg;
-        return ret;
+        if (unlikely(ret)) {
+                if (length == ios->length)
+                        return ret;
+                else
+                        ios->length -= length;
+        }
+        return 0;
 }
 
 int ore_create(struct ore_io_state *ios)