Patch for "Striped" read from AFR volumes

[Csibra Gergo <gergo@xxxxxxxxx>]

Hi,

apply following patch, to read AFR volumes like RAID0 volumes. The
current implementation of AFR reads every blocks from the first child
if that available. With this simple patch cycles through all available
childs. This meand every afr_readv calls reads from the next child
readed as previous call. So if U have 4 child, first block will be
readed from 1st next from 2nd next from 3rd next from 4th and starts
from first so next from 1st.

to apply this patch
cd xlators/cluster/afr/src
patch -p0 <afr_striped_read_1.3.7.diff
make
make install

patch also available here:
http://www.csibra.hu/glusterfs/afr_striped_read_1.3.7.diff

as you see this patch against 1.3.7 version.

here's the patch:
>>>>CUT HERE<<<<
*** /root/afr.c 2007-10-17 17:40:37.000000000 +0200
--- afr.c       2007-12-31 16:51:38.000000000 +0100
***************
*** 2448,2453 ****
--- 2448,2469 ----
        if (afrfdp->fdstate[i])
          break;
        }
+       if(i == pvt->child_count) {
+         // if we reached the last child, test if maybe there're unreaded child
+         data_t *fr = dict_get(local->fd->ctx, "first_read");
+       if(fr) {
+         int32_t frd = data_to_int32(fr);
+         // frd contains the first child what readed
+         if(frd > 0) {
+           // if first readed child was not the first physical child, start child search again
+           i = 0;
+           for (; i < pvt->child_count; i++) {
+             if (afrfdp->fdstate[i])
+               break;
+           }
+         }
+       }
+       }
        if (i < pvt->child_count) {
                STACK_WIND (frame,
                    afr_readv_cbk,
***************
*** 2492,2501 ****
    local->size = size;
    local->fd = fd;
  
!   for (i = 0; i < child_count; i++) {
      if (afrfdp->fdstate[i] && pvt->state[i])
        break;
    }
    if (i == child_count) {
      STACK_UNWIND (frame, -1, ENOTCONN, NULL, 0, NULL);
    } else {
--- 2508,2548 ----
    local->size = size;
    local->fd = fd;
  
!   int32_t next_child, first_read = 0;
!   data_t *nxtc = dict_get(fd->ctx, "next_child");
!   if(nxtc) {
!     next_child = data_to_int32(nxtc);
!   } else {
!     next_child = -1;
!     first_read = 1;
!   }
!   next_child++;
!   if(next_child == child_count) {
!     next_child = 0;
!   }
! 
!   for (i = next_child; i < child_count; i++) {
      if (afrfdp->fdstate[i] && pvt->state[i])
        break;
    }
+ 
+   if(i == child_count) {
+     i = 0;
+     for (i = 0; i < child_count; i++) {
+       if (afrfdp->fdstate[i] && pvt->state[i])
+       break;
+     }
+     if(i == child_count) {
+       next_child = 0;
+     } else {
+       next_child = i;
+     }
+   }
+   dict_set(fd->ctx, "next_child", data_from_int32(next_child));
+   if(first_read) {
+       dict_set(fd->ctx, "first_read", data_from_int32(i));
+   }
+ 
    if (i == child_count) {
      STACK_UNWIND (frame, -1, ENOTCONN, NULL, 0, NULL);
    } else {