exofs: Prepare for groups

* Rename _offset_dev_unit_off() to _calc_stripe_info()
  and recieve a struct for the output params

* In _prepare_for_striping we only need to call
  _calc_stripe_info() once. The other componets
  are easy to calculate from that. This code
  was inspired by what's done in truncate.

* Some code shifts that make sense now but will make
  more sense when group support is added.

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

1 files changed, 99 insertions, 60 deletions

diff --git a/fs/exofs/ios.c b/fs/exofs/ios.c
index 263052c77f41..d28febdf54ab 100644
--- a/fs/exofs/ios.c
+++ b/fs/exofs/ios.c
@@ -259,28 +259,46 @@ int exofs_check_io(struct exofs_io_state *ios, u64 *resid)
         return acumulated_lin_err;
 }
 
-/* REMOVEME: After review
-   Some quoteing from the standard
-
-   L = logical offset into the file
-   W = number of data components in a stripe
-   S = W * stripe_unit (S is Stripe length)
-   N = L / S (N is the stripe Number)
-   C = (L-(N*S)) / stripe_unit (C is the component)
-   O = (N*stripe_unit)+(L%stripe_unit) (O is the object's offset)
-*/
-
-static void _offset_dev_unit_off(struct exofs_io_state *ios, u64 file_offset,
-                        u64 *obj_offset, unsigned *dev, unsigned *unit_off)
+/*
+ * L - logical offset into the file
+ *
+ * U - The number of bytes in a full stripe
+ *
+ *      U = stripe_unit * group_width
+ *
+ * N - The stripe number
+ *
+ *      N = L / U
+ *
+ * C - The component index coresponding to L
+ *
+ *      C = (L - (N*U)) / stripe_unit
+ *
+ * O - The component offset coresponding to L
+ *
+ *      (N*stripe_unit)+(L%stripe_unit)
+ */
+
+struct _striping_info {
+        u64 obj_offset;
+        unsigned dev;
+        unsigned unit_off;
+};
+
+static void _calc_stripe_info(struct exofs_io_state *ios, u64 file_offset,
+                              struct _striping_info *si)
 {
-        unsigned stripe_unit = ios->layout->stripe_unit;
-        unsigned stripe_length = stripe_unit * ios->layout->group_width;
-        u64 stripe_no = file_offset;
-        unsigned stripe_mod = do_div(stripe_no, stripe_length);
+        u32     stripe_unit = ios->layout->stripe_unit;
+        u32     group_width = ios->layout->group_width;
+        u32     U = stripe_unit * group_width;
+
+        u32     LmodU;
+        u64     N = div_u64_rem(file_offset, U, &LmodU);
 
-        *unit_off = stripe_mod % stripe_unit;
-        *obj_offset = stripe_no * stripe_unit + *unit_off;
-        *dev = stripe_mod / stripe_unit * ios->layout->mirrors_p1;
+        si->unit_off = LmodU % stripe_unit;
+        si->obj_offset = N * stripe_unit + si->unit_off;
+        si->dev = LmodU / stripe_unit;
+        si->dev *= ios->layout->mirrors_p1;
 }
 
 static int _add_stripe_unit(struct exofs_io_state *ios,  unsigned *cur_pg,
@@ -327,65 +345,88 @@ static int _add_stripe_unit(struct exofs_io_state *ios,  unsigned *cur_pg,
         return 0;
 }
 
-static int _prepare_for_striping(struct exofs_io_state *ios)
+static int _prepare_pages(struct exofs_io_state *ios,
+                          struct _striping_info *si)
 {
         u64 length = ios->length;
-        u64 offset = ios->offset;
         unsigned stripe_unit = ios->layout->stripe_unit;
+        unsigned mirrors_p1 = ios->layout->mirrors_p1;
+        unsigned dev = si->dev;
         unsigned comp = 0;
         unsigned stripes = 0;
         unsigned cur_pg = 0;
         int ret = 0;
 
-        if (!ios->pages) {
-                if (ios->kern_buff) {
-                        struct exofs_per_dev_state *per_dev = &ios->per_dev[0];
-                        unsigned unit_off;
-
-                        _offset_dev_unit_off(ios, offset, &per_dev->offset,
-                                             &per_dev->dev, &unit_off);
-                        /* no cross device without page array */
-                        BUG_ON((ios->layout->group_width > 1) &&
-                               (unit_off + length > stripe_unit));
-                }
-                ios->numdevs = ios->layout->mirrors_p1;
-                return 0;
-        }
-
         while (length) {
                 struct exofs_per_dev_state *per_dev = &ios->per_dev[comp];
-                unsigned cur_len, page_off;
+                unsigned cur_len, page_off = 0;
 
                 if (!per_dev->length) {
-                        unsigned unit_off;
+                        per_dev->dev = dev;
+                        if (dev < si->dev) {
+                                per_dev->offset = si->obj_offset + stripe_unit -
+                                                                   si->unit_off;
+                                cur_len = stripe_unit;
+                        } else if (dev == si->dev) {
+                                per_dev->offset = si->obj_offset;
+                                cur_len = stripe_unit - si->unit_off;
+                                page_off = si->unit_off & ~PAGE_MASK;
+                                BUG_ON(page_off && (page_off != ios->pgbase));
+                        } else { /* dev > si->dev */
+                                per_dev->offset = si->obj_offset - si->unit_off;
+                                cur_len = stripe_unit;
+                        }
 
-                        _offset_dev_unit_off(ios, offset, &per_dev->offset,
-                                             &per_dev->dev, &unit_off);
                         stripes++;
-                        cur_len = min_t(u64, stripe_unit - unit_off, length);
-                        offset += cur_len;
-                        page_off = unit_off & ~PAGE_MASK;
-                        BUG_ON(page_off != ios->pgbase);
+
+                        dev += mirrors_p1;
+                        dev %= ios->layout->s_numdevs;
                 } else {
-                        cur_len = min_t(u64, stripe_unit, length);
-                        page_off = 0;
+                        cur_len = stripe_unit;
                 }
+                if (cur_len >= length)
+                        cur_len = length;
 
                 ret = _add_stripe_unit(ios, &cur_pg, page_off , per_dev,
                                        cur_len);
                 if (unlikely(ret))
                         goto out;
 
-                comp += ios->layout->mirrors_p1;
+                comp += mirrors_p1;
                 comp %= ios->layout->s_numdevs;
 
                 length -= cur_len;
         }
 out:
-        ios->numdevs = stripes * ios->layout->mirrors_p1;
+        ios->numdevs = stripes * mirrors_p1;
         return ret;
 }
 
+static int _prepare_for_striping(struct exofs_io_state *ios)
+{
+        struct _striping_info si;
+
+        _calc_stripe_info(ios, ios->offset, &si);
+
+        if (!ios->pages) {
+                if (ios->kern_buff) {
+                        struct exofs_per_dev_state *per_dev = &ios->per_dev[0];
+
+                        per_dev->offset = si.obj_offset;
+                        per_dev->dev = si.dev;
+
+                        /* no cross device without page array */
+                        BUG_ON((ios->layout->group_width > 1) &&
+                               (si.unit_off + ios->length >
+                                ios->layout->stripe_unit));
+                }
+                ios->numdevs = ios->layout->mirrors_p1;
+                return 0;
+        }
+
+        return _prepare_pages(ios, &si);
+}
+
 int exofs_sbi_create(struct exofs_io_state *ios)
 {
         int i, ret;
@@ -648,9 +689,7 @@ int exofs_oi_truncate(struct exofs_i_info *oi, u64 size)
                 struct osd_attr attr;
                 __be64 newsize;
         } *size_attrs;
-        u64 this_obj_size;
-        unsigned dev;
-        unsigned unit_off;
+        struct _striping_info si;
         int i, ret;
 
         ret = exofs_get_io_state(&sbi->layout, &ios);
@@ -668,19 +707,19 @@ int exofs_oi_truncate(struct exofs_i_info *oi, u64 size)
         ios->cred = oi->i_cred;
 
         ios->numdevs = ios->layout->s_numdevs;
-        _offset_dev_unit_off(ios, size, &this_obj_size, &dev, &unit_off);
+        _calc_stripe_info(ios, size, &si);
 
         for (i = 0; i < ios->layout->group_width; ++i) {
                 struct exofs_trunc_attr *size_attr = &size_attrs[i];
                 u64 obj_size;
 
-                if (i < dev)
-                        obj_size = this_obj_size +
-                                        ios->layout->stripe_unit - unit_off;
-                else if (i == dev)
-                        obj_size = this_obj_size;
-                else /* i > dev */
-                        obj_size = this_obj_size - unit_off;
+                if (i < si.dev)
+                        obj_size = si.obj_offset +
+                                        ios->layout->stripe_unit - si.unit_off;
+                else if (i == si.dev)
+                        obj_size = si.obj_offset;
+                else /* i > si.dev */
+                        obj_size = si.obj_offset - si.unit_off;
 
                 size_attr->newsize = cpu_to_be64(obj_size);
                 size_attr->attr = g_attr_logical_length;