[PATCH 03/13] perf: Simplify perf_fget_light()

Peter Zijlstra
2023-11-02T15:33:08Z

Introduce fdnull and use it to simplify perf_fget_light() to either
return a valid struct fd or not -- much like fdget() itself.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/file.h | 7 ++++++-
kernel/events/core.c | 22 +++++++++++-----------
2 files changed, 17 insertions(+), 12 deletions(-)

--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -59,6 +59,8 @@ static inline struct fd __to_fd(unsigned
return (struct fd){(struct file *)(v & ~3),v & 3};
}

+#define fdnull __to_fd(0)
+
static inline struct fd fdget(unsigned int fd)
{
return __to_fd(__fdget(fd));
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5802,18 +5802,17 @@ EXPORT_SYMBOL_GPL(perf_event_period);

static const struct file_operations perf_fops;

-static inline int perf_fget_light(int fd, struct fd *p)
+static inline struct fd perf_fdget(int fd)
{
struct fd f = fdget(fd);
if (!f.file)
- return -EBADF;
+ return fdnull;

if (f.file->f_op != &perf_fops) {
fdput(f);
- return -EBADF;
+ return fdnull;
}
- *p = f;
- return 0;
+ return f;
}

static int perf_event_set_output(struct perf_event *event,
@@ -5864,10 +5863,9 @@ static long _perf_ioctl(struct perf_even
int ret;
if (arg != -1) {
struct perf_event *output_event;
- struct fd output;
- ret = perf_fget_light(arg, &output);
- if (ret)
- return ret;
+ struct fd output = perf_fdget(arg);
+ if (!output.file)
+ return -EBADF;
output_event = output.file->private_data;
ret = perf_event_set_output(event, output_event);
fdput(output);
@@ -12401,9 +12399,11 @@ SYSCALL_DEFINE5(perf_event_open,
return event_fd;

if (group_fd != -1) {
- err = perf_fget_light(group_fd, &group);
- if (err)
+ group = perf_fdget(group_fd);
+ if (!group.file) {
+ err = -EBADF;
goto err_fd;
+ }
group_leader = group.file->private_data;
if (flags & PERF_FLAG_FD_OUTPUT)
output_event = group_leader;