linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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


  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)

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200107175927.4558-2-sargun@sargun.me \
    --to=sargun@sargun.me \
    --cc=arnd@arndb.de \
    --cc=christian.brauner@ubuntu.com \
    --cc=containers@lists.linux-foundation.org \
    --cc=cyphar@cyphar.com \
    --cc=ealvarez@mozilla.com \
    --cc=fweimer@redhat.com \
    --cc=gpascutto@mozilla.com \
    --cc=jannh@google.com \
    --cc=jld@mozilla.com \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@amacapital.net \
    --cc=oleg@redhat.com \
    --cc=tycho@tycho.ws \
    --cc=viro@zeniv.linux.org.uk \
    --subject='Re: [PATCH v9 1/4] vfs, fdtable: Add fget_task helper' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox