make domain_create() return a proper error code

While triggered by the XSA-9 fix, this really is of more general use;
that fix just pointed out very sharply that the current situation
with all domain creation failures reported to user (tools) space as
-ENOMEM is very unfortunate (actively misleading users _and_ support
personnel).

Pull over the pointer <-> error code conversion infrastructure from
Linux, and use it in domain_create() and all it callers.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -26,6 +26,7 @@
 #include <xen/serial.h>
 #include <xen/sched.h>
 #include <xen/console.h>
+#include <xen/err.h>
 #include <xen/init.h>
 #include <xen/irq.h>
 #include <xen/mm.h>
@@ -237,7 +238,7 @@ void __init start_xen(unsigned long boot
 
     /* Create initial domain 0. */
     dom0 = domain_create(0, 0, 0);
-    if ( dom0 == NULL )
+    if ( IS_ERR(dom0) )
             printk("domain_create failed\n");
     if ( (dom0 == NULL) || (alloc_dom0_vcpu0() == NULL) )
             panic("Error creating domain 0\n");
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -91,7 +91,7 @@
 #include <xen/mm.h>
 #include <xen/domain.h>
 #include <xen/sched.h>
-#include <xen/errno.h>
+#include <xen/err.h>
 #include <xen/perfc.h>
 #include <xen/irq.h>
 #include <xen/softirq.h>
@@ -309,7 +309,7 @@ void __init arch_init_memory(void)
      * their domain field set to dom_xen.
      */
     dom_xen = domain_create(DOMID_XEN, DOMCRF_dummy, 0);
-    BUG_ON(dom_xen == NULL);
+    BUG_ON(IS_ERR(dom_xen));
 
     /*
      * Initialise our DOMID_IO domain.
@@ -317,14 +317,14 @@ void __init arch_init_memory(void)
      * array. Mappings occur at the priv of the caller.
      */
     dom_io = domain_create(DOMID_IO, DOMCRF_dummy, 0);
-    BUG_ON(dom_io == NULL);
+    BUG_ON(IS_ERR(dom_io));
     
     /*
-     * Initialise our DOMID_IO domain.
+     * Initialise our COW domain.
      * This domain owns sharable pages.
      */
     dom_cow = domain_create(DOMID_COW, DOMCRF_dummy, 0);
-    BUG_ON(dom_cow == NULL);
+    BUG_ON(IS_ERR(dom_cow));
 
     /* First 1MB of RAM is historically marked as I/O. */
     for ( i = 0; i < 0x100; i++ )
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1,6 +1,7 @@
 #include <xen/config.h>
 #include <xen/init.h>
 #include <xen/lib.h>
+#include <xen/err.h>
 #include <xen/sched.h>
 #include <xen/sched-if.h>
 #include <xen/domain.h>
@@ -1319,7 +1320,7 @@ void __init __start_xen(unsigned long mb
 
     /* Create initial domain 0. */
     dom0 = domain_create(0, DOMCRF_s3_integrity, 0);
-    if ( (dom0 == NULL) || (alloc_dom0_vcpu0() == NULL) )
+    if ( IS_ERR(dom0) || (alloc_dom0_vcpu0() == NULL) )
         panic("Error creating domain 0\n");
 
     dom0->is_privileged = 1;
--- a/xen/common/cpupool.c
+++ b/xen/common/cpupool.c
@@ -370,14 +370,18 @@ out:
 int cpupool_add_domain(struct domain *d, int poolid)
 {
     struct cpupool *c;
-    int rc = 1;
+    int rc;
     int n_dom = 0;
 
     if ( poolid == CPUPOOLID_NONE )
         return 0;
     spin_lock(&cpupool_lock);
     c = cpupool_find_by_id(poolid);
-    if ( (c != NULL) && cpumask_weight(c->cpu_valid) )
+    if ( c == NULL )
+        rc = -ESRCH;
+    else if ( !cpumask_weight(c->cpu_valid) )
+        rc = -ENODEV;
+    else
     {
         c->n_dom++;
         n_dom = c->n_dom;
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -9,7 +9,7 @@
 #include <xen/init.h>
 #include <xen/lib.h>
 #include <xen/ctype.h>
-#include <xen/errno.h>
+#include <xen/err.h>
 #include <xen/sched.h>
 #include <xen/sched-if.h>
 #include <xen/domain.h>
@@ -196,17 +196,17 @@ struct domain *domain_create(
     struct domain *d, **pd;
     enum { INIT_xsm = 1u<<0, INIT_watchdog = 1u<<1, INIT_rangeset = 1u<<2,
            INIT_evtchn = 1u<<3, INIT_gnttab = 1u<<4, INIT_arch = 1u<<5 };
-    int init_status = 0;
+    int err, init_status = 0;
     int poolid = CPUPOOLID_NONE;
 
     if ( (d = alloc_domain_struct()) == NULL )
-        return NULL;
+        return ERR_PTR(-ENOMEM);
 
     d->domain_id = domid;
 
     lock_profile_register_struct(LOCKPROF_TYPE_PERDOM, d, domid, "Domain");
 
-    if ( xsm_alloc_security_domain(d) != 0 )
+    if ( (err = xsm_alloc_security_domain(d)) != 0 )
         goto fail;
     init_status |= INIT_xsm;
 
@@ -226,6 +226,7 @@ struct domain *domain_create(
     spin_lock_init(&d->shutdown_lock);
     d->shutdown_code = -1;
 
+    err = -ENOMEM;
     if ( !zalloc_cpumask_var(&d->domain_dirty_cpumask) )
         goto fail;
 
@@ -251,7 +252,7 @@ struct domain *domain_create(
 
     if ( !is_idle_domain(d) )
     {
-        if ( xsm_domain_create(d, ssidref) != 0 )
+        if ( (err = xsm_domain_create(d, ssidref)) != 0 )
             goto fail;
 
         d->is_paused_by_controller = 1;
@@ -266,29 +267,30 @@ struct domain *domain_create(
 
         radix_tree_init(&d->pirq_tree);
 
-        if ( evtchn_init(d) != 0 )
+        if ( (err = evtchn_init(d)) != 0 )
             goto fail;
         init_status |= INIT_evtchn;
 
-        if ( grant_table_create(d) != 0 )
+        if ( (err = grant_table_create(d)) != 0 )
             goto fail;
         init_status |= INIT_gnttab;
 
         poolid = 0;
 
+        err = -ENOMEM;
         d->mem_event = xzalloc(struct mem_event_per_domain);
         if ( !d->mem_event )
             goto fail;
     }
 
-    if ( arch_domain_create(d, domcr_flags) != 0 )
+    if ( (err = arch_domain_create(d, domcr_flags)) != 0 )
         goto fail;
     init_status |= INIT_arch;
 
-    if ( cpupool_add_domain(d, poolid) != 0 )
+    if ( (err = cpupool_add_domain(d, poolid)) != 0 )
         goto fail;
 
-    if ( sched_init_domain(d) != 0 )
+    if ( (err = sched_init_domain(d)) != 0 )
         goto fail;
 
     if ( !is_idle_domain(d) )
@@ -329,7 +331,7 @@ struct domain *domain_create(
         xsm_free_security_domain(d);
     free_cpumask_var(d->domain_dirty_cpumask);
     free_domain_struct(d);
-    return NULL;
+    return ERR_PTR(err);
 }
 
 
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -9,6 +9,7 @@
 #include <xen/config.h>
 #include <xen/types.h>
 #include <xen/lib.h>
+#include <xen/err.h>
 #include <xen/mm.h>
 #include <xen/sched.h>
 #include <xen/sched-if.h>
@@ -455,10 +456,12 @@ long do_domctl(XEN_GUEST_HANDLE(xen_domc
         if ( op->u.createdomain.flags & XEN_DOMCTL_CDF_oos_off )
             domcr_flags |= DOMCRF_oos_off;
 
-        ret = -ENOMEM;
         d = domain_create(dom, domcr_flags, op->u.createdomain.ssidref);
-        if ( d == NULL )
+        if ( IS_ERR(d) )
+        {
+            ret = PTR_ERR(d);
             break;
+        }
 
         ret = 0;
 
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -28,7 +28,7 @@
 #include <xen/softirq.h>
 #include <xen/trace.h>
 #include <xen/mm.h>
-#include <xen/errno.h>
+#include <xen/err.h>
 #include <xen/guest_access.h>
 #include <xen/multicall.h>
 #include <xen/cpu.h>
@@ -1323,7 +1323,7 @@ void __init scheduler_init(void)
         panic("scheduler returned error on init\n");
 
     idle_domain = domain_create(DOMID_IDLE, 0, 0);
-    BUG_ON(idle_domain == NULL);
+    BUG_ON(IS_ERR(idle_domain));
     idle_domain->vcpu = idle_vcpu;
     idle_domain->max_vcpus = nr_cpu_ids;
     if ( alloc_vcpu(idle_domain, 0, 0) == NULL )
--- /dev/null
+++ b/xen/include/xen/err.h
@@ -0,0 +1,57 @@
+#if !defined(__XEN_ERR_H__) && !defined(__ASSEMBLY__)
+#define __XEN_ERR_H__
+
+#include <xen/compiler.h>
+#include <xen/errno.h>
+
+/*
+ * Kernel pointers have redundant information, so we can use a
+ * scheme where we can return either an error code or a dentry
+ * pointer with the same return value.
+ *
+ * This could be a per-architecture thing, to allow different
+ * error and pointer decisions.
+ */
+#define MAX_ERRNO	4095
+
+#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
+
+static inline void *__must_check ERR_PTR(long error)
+{
+	return (void *)error;
+}
+
+static inline long __must_check PTR_ERR(const void *ptr)
+{
+	return (long)ptr;
+}
+
+static inline long __must_check IS_ERR(const void *ptr)
+{
+	return IS_ERR_VALUE((unsigned long)ptr);
+}
+
+static inline long __must_check IS_ERR_OR_NULL(const void *ptr)
+{
+	return !ptr || IS_ERR_VALUE((unsigned long)ptr);
+}
+
+/**
+ * ERR_CAST - Explicitly cast an error-valued pointer to another pointer type
+ * @ptr: The pointer to cast.
+ *
+ * Explicitly cast an error-valued pointer to another pointer type in such a
+ * way as to make it clear that's what's going on.
+ */
+static inline void * __must_check ERR_CAST(const void *ptr)
+{
+	/* cast away the const */
+	return (void *)ptr;
+}
+
+static inline int __must_check PTR_RET(const void *ptr)
+{
+	return IS_ERR(ptr) ? PTR_ERR(ptr) : 0;
+}
+
+#endif /* __XEN_ERR_H__ */