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>

diff --git a/fs/exofs/ore.c b/fs/exofs/ore.c
index d0f8db5e46c5ce6ed75fec917476e50a7db0ece2..8354fe061d1ce87e9036666ad1a7ec5b836d6af0 100644 (file)
--- 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)