From: Sargun Dhillon <sargun@sargun.me>
To: linux-kernel@vger.kernel.org,
containers@lists.linux-foundation.org, linux-api@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Cc: Sargun Dhillon <sargun@sargun.me>,
tycho@tycho.ws, jannh@google.com, cyphar@cyphar.com,
christian.brauner@ubuntu.com, oleg@redhat.com,
luto@amacapital.net, viro@zeniv.linux.org.uk,
gpascutto@mozilla.com, ealvarez@mozilla.com, fweimer@redhat.com,
jld@mozilla.com, arnd@arndb.de
Subject: [PATCH v9 1/4] vfs, fdtable: Add fget_task helper
Date: Tue, 7 Jan 2020 09:59:24 -0800 [thread overview]
Message-ID: <20200107175927.4558-2-sargun@sargun.me> (raw)
In-Reply-To: <20200107175927.4558-1-sargun@sargun.me>
This introduces a function which can be used to fetch a file, given an
arbitrary task. As long as the user holds a reference (refcnt) to the
task_struct it is safe to call, and will either return NULL on failure,
or a pointer to the file, with a refcnt.
This patch is based on Oleg Nesterov's (cf. [1]) patch from September
2018.
[1]: Link: https://lore.kernel.org/r/20180915160423.GA31461@redhat.com
Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
fs/file.c | 22 ++++++++++++++++++++--
include/linux/file.h | 2 ++
2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/fs/file.c b/fs/file.c
index 2f4fcf985079..2fc5eeef54a4 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -706,9 +706,9 @@ void do_close_on_exec(struct files_struct *files)
spin_unlock(&files->file_lock);
}
-static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
+static struct file *__fget_files(struct files_struct *files, unsigned int fd,
+ fmode_t mask, unsigned int refs)
{
- struct files_struct *files = current->files;
struct file *file;
rcu_read_lock();
@@ -729,6 +729,12 @@ static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
return file;
}
+static inline struct file *__fget(unsigned int fd, fmode_t mask,
+ unsigned int refs)
+{
+ return __fget_files(current->files, fd, mask, refs);
+}
+
struct file *fget_many(unsigned int fd, unsigned int refs)
{
return __fget(fd, FMODE_PATH, refs);
@@ -746,6 +752,18 @@ struct file *fget_raw(unsigned int fd)
}
EXPORT_SYMBOL(fget_raw);
+struct file *fget_task(struct task_struct *task, unsigned int fd)
+{
+ struct file *file = NULL;
+
+ task_lock(task);
+ if (task->files)
+ file = __fget_files(task->files, fd, 0, 1);
+ task_unlock(task);
+
+ return file;
+}
+
/*
* Lightweight file lookup - no refcnt increment if fd table isn't shared.
*
diff --git a/include/linux/file.h b/include/linux/file.h
index 3fcddff56bc4..c6c7b24ea9f7 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -16,6 +16,7 @@ extern void fput(struct file *);
extern void fput_many(struct file *, unsigned int);
struct file_operations;
+struct task_struct;
struct vfsmount;
struct dentry;
struct inode;
@@ -47,6 +48,7 @@ static inline void fdput(struct fd fd)
extern struct file *fget(unsigned int fd);
extern struct file *fget_many(unsigned int fd, unsigned int refs);
extern struct file *fget_raw(unsigned int fd);
+extern struct file *fget_task(struct task_struct *task, unsigned int fd);
extern unsigned long __fdget(unsigned int fd);
extern unsigned long __fdget_raw(unsigned int fd);
extern unsigned long __fdget_pos(unsigned int fd);
--
2.20.1
next prev parent reply other threads:[~2020-01-07 17:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-07 17:59 [PATCH v9 0/4] Add pidfd_getfd syscall Sargun Dhillon
2020-01-07 17:59 ` Sargun Dhillon [this message]
2020-01-13 15:02 ` [PATCH v9 1/4] vfs, fdtable: Add fget_task helper Arnd Bergmann
2020-01-07 17:59 ` [PATCH v9 2/4] pid: Implement pidfd_getfd syscall Sargun Dhillon
2020-01-13 14:58 ` Arnd Bergmann
2020-01-07 17:59 ` [PATCH v9 3/4] arch: wire up " Sargun Dhillon
2020-01-13 14:59 ` Arnd Bergmann
2020-01-07 17:59 ` [PATCH v9 4/4] test: Add test for pidfd getfd Sargun Dhillon
2020-01-07 20:54 ` [PATCH v9 0/4] Add pidfd_getfd syscall Christian Brauner
2020-01-10 11:40 ` Christian Brauner
2020-03-31 20:11 ` RFC: pidfd_getfd(2) manual page Michael Kerrisk (man-pages)
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