block: add ioprio_check_cap function

Aio per command iopriority support introduces a second interface between
userland and the kernel capable of passing iopriority. The aio interface also
needs the ability to verify that the submitting context has sufficient
privileges to submit IOPRIO_RT commands. This patch creates the
ioprio_check_cap function to be used by the ioprio_set system call and also by
the aio interface.

Signed-off-by: Adam Manzanares <adam.manzanares@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 18 insertions, 6 deletions

diff --git a/block/ioprio.c b/block/ioprio.c
index 6f5d0b6625e3..f9821080c92c 100644
--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -61,15 +61,10 @@ int set_task_ioprio(struct task_struct *task, int ioprio)
 }
 EXPORT_SYMBOL_GPL(set_task_ioprio);
 
-SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
+int ioprio_check_cap(int ioprio)
 {
         int class = IOPRIO_PRIO_CLASS(ioprio);
         int data = IOPRIO_PRIO_DATA(ioprio);
-        struct task_struct *p, *g;
-        struct user_struct *user;
-        struct pid *pgrp;
-        kuid_t uid;
-        int ret;
 
         switch (class) {
                 case IOPRIO_CLASS_RT:
@@ -92,6 +87,21 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
                         return -EINVAL;
         }
 
+        return 0;
+}
+
+SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
+{
+        struct task_struct *p, *g;
+        struct user_struct *user;
+        struct pid *pgrp;
+        kuid_t uid;
+        int ret;
+
+        ret = ioprio_check_cap(ioprio);
+        if (ret)
+                return ret;
+
         ret = -ESRCH;
         rcu_read_lock();
         switch (which) {
diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
index 627efac73e6d..4a28cec49ec3 100644
--- a/include/linux/ioprio.h
+++ b/include/linux/ioprio.h
@@ -77,4 +77,6 @@ extern int ioprio_best(unsigned short aprio, unsigned short bprio);
 
 extern int set_task_ioprio(struct task_struct *task, int ioprio);
 
+extern int ioprio_check_cap(int ioprio);
+
 #endif