perfmon2 minimal: context creation

Index: o/perfmon/perfmon_ctx.c
===================================================================
@@ -162,3 +162,180 @@
 	}
 	return 0;
 }
+
+/**
+ * pfm_ctx_permissions - check authorization to create new context
+ * @ctx_flags: context flags passed by user
+ *
+ * check for permissions to create a context.
+ *
+ * A sysadmin may decide to restrict creation of per-thread
+ * context to a group of users using the group id via
+ * /sys/kernel/perfmon/task_group
+ *
+ * Once we identify a user level package which can be used
+ * to grant/revoke Linux capabilites at login via PAM, we will
+ * be able to use capabilities. We would also need to increase
+ * the size of cap_t to support more than 32 capabilities (it
+ * is currently defined as u32 and 32 capabilities are alrady
+ * defined).
+ */
+static inline int pfm_ctx_permissions(u32 ctx_flags)
+{
+	if (pfm_controls.task_group != PFM_GROUP_PERM_ANY
+		   && !in_group_p(pfm_controls.task_group)) {
+		PFM_DBG("user group not allowed to create a task context");
+		return -EPERM;
+	}
+	return 0;
+}
+
+/**
+ * pfm_create_initial_set - create initial set from __pfm_c reate_context
+ * @ctx: context to atatched the set to
+ */
+static void pfm_create_initial_set(struct pfm_context *ctx)
+{
+	struct pfm_event_set *set;
+	u64 *impl_pmcs;
+	u16 i, max_pmc;
+
+	set = ctx->active_set;
+	max_pmc = pfm_pmu_conf->regs.max_pmc;
+	impl_pmcs =  pfm_pmu_conf->regs.pmcs;
+
+	/*
+	 * install default values for all PMC  registers
+	 */
+	for (i = 0; i < max_pmc; i++) {
+		if (test_bit(i, cast_ulp(impl_pmcs))) {
+			set->pmcs[i] = pfm_pmu_conf->pmc_desc[i].dfl_val;
+			PFM_DBG("pmc%u=0x%llx",
+				i,
+				(unsigned long long)set->pmcs[i]);
+		}
+	}
+	/*
+	 * PMD registers are set to 0 when the event set is allocated,
+	 * hence we do not need to explicitly initialize them.
+	 *
+	 * For virtual PMD registers (i.e., those tied to a SW resource)
+	 * their value becomes meaningful once the context is attached.
+	 */
+}
+
+/**
+ * __pfm_create_context - allocate and initialize a perfmon context
+ * @ctx_flags : user context flags
+ *
+ * function used to allocate a new context. A context is allocated along
+ * with the default event set. If a sampling format is used, the buffer
+ * may be allocated and initialized.
+ *
+ * The file descriptor identifying the context is allocated and returned
+ * to caller.
+ *
+ * This function operates with no locks and interrupts are enabled.
+ * return:
+ * 	>=0: the file descriptor to identify the context
+ * 	<0 : the error code
+ */
+int __pfm_create_context(__u32 ctx_flags)
+{
+	struct pfm_context *ctx;
+	struct file *filp = NULL;
+	int fd = 0, ret = -EINVAL;
+
+	if (!pfm_pmu_conf)
+		return -ENOSYS;
+
+	/* no context flags supported yet */
+	if (ctx_flags)
+		goto error_alloc;
+
+	ret = pfm_ctx_permissions(ctx_flags);
+	if (ret < 0)
+		goto error_alloc;
+
+	/*
+	 * we can use GFP_KERNEL and potentially sleep because we do
+	 * not hold any lock at this point.
+	 */
+	might_sleep();
+	ret = -ENOMEM;
+	ctx = kmem_cache_zalloc(pfm_ctx_cachep, GFP_KERNEL);
+	if (!ctx)
+		goto error_alloc;
+
+	PFM_DBG("alloc ctx @0x%p", ctx);
+
+	ctx->active_set = &ctx->_set0;
+
+	spin_lock_init(&ctx->lock);
+
+	ret = pfm_pmu_acquire();
+	if (ret)
+		goto error_file;
+	/*
+	 * check if PMU is usable
+	 */
+	if (!(pfm_pmu_conf->regs.num_pmcs && pfm_pmu_conf->regs.num_pmcs)) {
+		PFM_DBG("no usable PMU registers");
+		ret = -EBUSY;
+		goto error_file;
+	}
+
+	ret = -ENFILE;
+	fd = pfm_alloc_fd(&filp);
+	if (fd < 0)
+		goto error_file;
+
+	/*
+	 * context is unloaded
+	 */
+	ctx->state = PFM_CTX_UNLOADED;
+
+	/*
+	 * initialize arch-specific section
+	 * must be done before fmt_init()
+	 */
+	ret = pfm_arch_context_create(ctx, ctx_flags);
+	if (ret)
+		goto error_set;
+
+	ret = -ENOMEM;
+
+	/*
+	 * add initial set
+	 */
+	pfm_create_initial_set(ctx);
+
+	filp->private_data = ctx;
+
+	ctx->last_act = PFM_INVALID_ACTIVATION;
+	ctx->last_cpu = -1;
+
+	PFM_DBG("flags=0x%x fd=%d", ctx_flags, fd);
+
+	/*
+	 * we defer the fd_install until we are certain the call succeeded
+	 * to ensure we do not have to undo its effect. Neither put_filp()
+	 * nor put_unused_fd() undoes the effect of fd_install().
+	 */
+	fd_install(fd, filp);
+
+	return fd;
+
+error_set:
+	put_filp(filp);
+	put_unused_fd(fd);
+error_file:
+	/*
+	 * calls the right *_put() functions
+	 * calls pfm_release_pmu()
+	 */
+	pfm_free_context(ctx);
+	return ret;
+error_alloc:
+	return ret;
+}

Index: o/perfmon/perfmon_priv.h
===================================================================
@@ -55,6 +55,7 @@
 
 int  pfm_init_sysfs(void);
 
+int __pfm_create_context(__u32 ctx_flags);
 void pfm_free_context(struct pfm_context *ctx);
 
 int __pfm_stop(struct pfm_context *ctx);

@@ -63,6 +64,8 @@
 int __pfm_load_context(struct pfm_context *ctx, struct task_struct *task);
 int __pfm_unload_context(struct pfm_context *ctx);
 
+int pfm_alloc_fd(struct file **cfile);
+
 ssize_t pfm_sysfs_res_show(char *buf, size_t sz, int what);
 
 int pfm_pmu_acquire(void);

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