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From:   "Eric W. Biederman" <ebiederm@xmission.com>
To:     linux-kernel@vger.kernel.org
Cc:     linux-fsdevel@vger.kernel.org, criu@openvz.org,
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        KP Singh <kpsingh@chromium.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>
Date:   Mon, 17 Aug 2020 17:04:14 -0500
Message-Id: <20200817220425.9389-6-ebiederm@xmission.com>
In-Reply-To: <87ft8l6ic3.fsf@x220.int.ebiederm.org>
References: <87ft8l6ic3.fsf@x220.int.ebiederm.org>
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Subject: [PATCH 06/17] file: Implement fcheck_task
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

As a companion to fget_task implement fcheck_task for use for querying
a process about a specific file.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/file.c               | 13 +++++++++++++
 include/linux/fdtable.h |  1 +
 2 files changed, 14 insertions(+)

diff --git a/fs/file.c b/fs/file.c
index c585dbaf31a3..8d4b385055e9 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -863,6 +863,19 @@ struct file *fget_task(struct task_struct *task, unsigned int fd)
 	return file;
 }
 
+struct file *fcheck_task(struct task_struct *task, unsigned int fd)
+{
+	/* Must be called with rcu_read_lock held */
+	struct file *file = NULL;
+
+	task_lock(task);
+	if (task->files)
+		file = fcheck_files(task->files, fd);
+	task_unlock(task);
+
+	return file;
+}
+
 /*
  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
  *
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 7cc9885044d9..def9debd2ce2 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -103,6 +103,7 @@ static inline struct file *fcheck_files(struct files_struct *files, unsigned int
  * Check whether the specified fd has an open file.
  */
 #define fcheck(fd)	fcheck_files(current->files, fd)
+struct file *fcheck_task(struct task_struct *task, unsigned int fd);
 
 struct task_struct;
 
-- 
2.25.0