linux-kernel - [PATCH 03/13] perf: Simplify perf_fget

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Message-Id: <20231102152018.069585432@infradead.org>
Date:   Thu, 02 Nov 2023 16:09:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
        namhyung@...nel.org, irogers@...gle.com, adrian.hunter@...el.com
Subject: [PATCH 03/13] perf: Simplify perf_fget_light()

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@...radead.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;