bitkeeper revision 1.1159.1.216 (41656f2ek7HkbBXpAt8AAbtJEyjlTg)

Grant-table interface redone. 

1 files changed, 32 insertions, 103 deletions

diff --git a/linux-2.6.8.1-xen-sparse/arch/xen/kernel/gnttab.c b/linux-2.6.8.1-xen-sparse/arch/xen/kernel/gnttab.c
index c76df4b1e4..af892aeb2a 100644
--- a/linux-2.6.8.1-xen-sparse/arch/xen/kernel/gnttab.c
+++ b/linux-2.6.8.1-xen-sparse/arch/xen/kernel/gnttab.c
@@ -33,22 +33,9 @@ EXPORT_SYMBOL(gnttab_end_foreign_access);
 EXPORT_SYMBOL(gnttab_grant_foreign_transfer);
 EXPORT_SYMBOL(gnttab_end_foreign_transfer);
 
-struct gntent_auxinfo {
-    u16         write_pin, read_pin; /* reference counts */
-    u16         inuse;
-    grant_ref_t next;                /* hash chain       */
-};
-
 #define NR_GRANT_REFS 512
-
-static struct gntent_auxinfo auxtab[NR_GRANT_REFS];
+static grant_ref_t gnttab_free_list[NR_GRANT_REFS];
 static grant_ref_t gnttab_free_head;
-static spinlock_t gnttab_lock;
-
-#define HASH_INVALID (0xFFFFU)
-#define GNTTAB_HASH_SZ 512
-#define GNTTAB_HASH(_f) ((_f) & (GNTTAB_HASH_SZ-1))
-static grant_ref_t gnttab_hash[GNTTAB_HASH_SZ];
 
 static grant_entry_t *shared;
 
@@ -56,14 +43,14 @@ static grant_entry_t *shared;
  * Lock-free grant-entry allocator
  */
 
-static inline grant_ref_t
+static inline int
 get_free_entry(
     void)
 {
     grant_ref_t fh, nfh = gnttab_free_head;
-    do { fh = nfh; }
+    do { if ( unlikely((fh = nfh) == NR_GRANT_REFS) ) return -1; }
     while ( unlikely((nfh = cmpxchg(&gnttab_free_head, fh,
-                                    auxtab[fh].next)) != fh) );
+                                    gnttab_free_list[fh])) != fh) );
     return fh;
 }
 
@@ -72,109 +59,55 @@ put_free_entry(
     grant_ref_t ref)
 {
     grant_ref_t fh, nfh = gnttab_free_head;
-    do { auxtab[ref].next = fh = nfh; wmb(); }
+    do { gnttab_free_list[ref] = fh = nfh; wmb(); }
     while ( unlikely((nfh = cmpxchg(&gnttab_free_head, fh, ref)) != fh) );
 }
 
 /*
- * Public interface functions
+ * Public grant-issuing interface functions
  */
 
-grant_ref_t
+int
 gnttab_grant_foreign_access(
     domid_t domid, unsigned long frame, int readonly)
 {
-    unsigned long flags;
-    grant_ref_t   ref;
-
-    spin_lock_irqsave(&gnttab_lock, flags);
-
-    for ( ref  = gnttab_hash[GNTTAB_HASH(frame)];
-          ref != HASH_INVALID;
-          ref  = auxtab[ref].next )
-    {
-        if ( auxtab[ref].inuse && (shared[ref].frame == frame) )
-        {
-            if ( readonly )
-                auxtab[ref].read_pin++;
-            else if ( auxtab[ref].write_pin++ == 0 )
-                clear_bit(_GTF_readonly, (unsigned long *)&shared[ref].flags);
-            goto done;
-        }
-    }
-
-    ref = get_free_entry();
-    auxtab[ref].inuse     = 1;
-    auxtab[ref].read_pin  = !!readonly;
-    auxtab[ref].write_pin =  !readonly;
-    auxtab[ref].next = gnttab_hash[GNTTAB_HASH(frame)];
-    gnttab_hash[GNTTAB_HASH(frame)] = ref;
+    int ref;
+    
+    if ( unlikely((ref = get_free_entry()) == -1) )
+        return -ENOSPC;
 
     shared[ref].frame = frame;
     shared[ref].domid = domid;
     wmb();
     shared[ref].flags = GTF_permit_access | (readonly ? GTF_readonly : 0);
 
- done:
-    spin_unlock_irqrestore(&gnttab_lock, flags);
-    return 0;
+    return ref;
 }
 
 void
 gnttab_end_foreign_access(
     grant_ref_t ref, int readonly)
 {
-    unsigned long flags, frame = shared[ref].frame;
-    grant_ref_t  *pref;
-    u16           sflags, nsflags;
-
-    spin_lock_irqsave(&gnttab_lock, flags);
+    u16 flags, nflags;
 
-    if ( readonly )
-    {
-        if ( (auxtab[ref].read_pin-- == 0) && (auxtab[ref].write_pin == 0) )
-            goto delete;
-    }
-    else if ( auxtab[ref].write_pin-- == 0 )
-    {
-        if ( auxtab[ref].read_pin == 0 )
-            goto delete;
-        nsflags = shared[ref].flags;
-        do {
-            if ( (sflags = nsflags) & GTF_writing )
-                printk(KERN_ALERT "WARNING: g.e. still in use for writing!\n");
-        }
-        while ( (nsflags = cmpxchg(&shared[ref].flags, sflags, 
-                                   sflags | GTF_readonly)) != sflags );
-    }
-
-    goto out;
-
- delete:
-    nsflags = shared[ref].flags;
+    nflags = shared[ref].flags;
     do {
-        if ( (sflags = nsflags) & (GTF_reading|GTF_writing) )
+        if ( (flags = nflags) & (GTF_reading|GTF_writing) )
             printk(KERN_ALERT "WARNING: g.e. still in use!\n");
     }
-    while ( (nsflags = cmpxchg(&shared[ref].flags, sflags, 0)) != sflags );
+    while ( (nflags = cmpxchg(&shared[ref].flags, flags, 0)) != flags );
 
-    pref = &gnttab_hash[GNTTAB_HASH(frame)];
-    while ( *pref != ref )
-        pref = &auxtab[*pref].next;
-    *pref = auxtab[ref].next;
-
-    auxtab[ref].inuse = 0;
     put_free_entry(ref);
-
- out:
-    spin_unlock_irqrestore(&gnttab_lock, flags);
 }
 
-grant_ref_t
+int
 gnttab_grant_foreign_transfer(
     domid_t domid)
 {
-    grant_ref_t ref = get_free_entry();
+    int ref;
+
+    if ( unlikely((ref = get_free_entry()) == -1) )
+        return -ENOSPC;
 
     shared[ref].frame = 0;
     shared[ref].domid = domid;
@@ -210,23 +143,19 @@ gnttab_end_foreign_transfer(
 
 void __init gnttab_init(void)
 {
-    int               i;
-    gnttab_op_t       gntop;
-    unsigned long     frame;
-
-    spin_lock_init(&gnttab_lock);
+    gnttab_setup_table_t setup;
+    unsigned long        frame;
+    int                  i;
 
-    for ( i = 0; i < GNTTAB_HASH_SZ; i++ )
-    {
-        gnttab_hash[i] = HASH_INVALID;
-        auxtab[i].next = i+1;
-    }
+    for ( i = 0; i < NR_GRANT_REFS; i++ )
+        gnttab_free_list[i] = i + 1;
 
-    gntop.cmd = GNTTABOP_setup_table;
-    gntop.u.setup_table.dom        = DOMID_SELF;
-    gntop.u.setup_table.nr_frames  = 1;
-    gntop.u.setup_table.frame_list = &frame;
-    if ( HYPERVISOR_grant_table_op(&gntop) != 0 )
+    setup.dom        = DOMID_SELF;
+    setup.nr_frames  = 1;
+    setup.frame_list = &frame;
+    if ( HYPERVISOR_grant_table_op(GNTTABOP_setup_table, &setup, 1) != 0 )
+        BUG();
+    if ( setup.status != 0 )
         BUG();
 
     set_fixmap_ma(FIX_GNTTAB, frame << PAGE_SHIFT);