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.
Signed-off-by: Sargun Dhillon <[email protected]>
---
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..0ceeb046f4f3 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 +729,11 @@ static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
return file;
}
+static 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 +751,19 @@ 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
On Mon, Dec 23, 2019 at 09:08:55PM +0000, Sargun Dhillon wrote:
> 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.
>
> Signed-off-by: Sargun Dhillon <[email protected]>
> ---
> 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..0ceeb046f4f3 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 +729,11 @@ static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
> return file;
> }
>
> +static 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 +751,19 @@ 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);
Nit: remove the \n:
task_lock(task);
if (task->files)
file = __fget_files(task->files, fd, 0, 1);
task_unlock(task);
Christian
On Mon, Dec 23, 2019 at 10:26:46PM +0100, Christian Brauner wrote:
> On Mon, Dec 23, 2019 at 09:08:55PM +0000, Sargun Dhillon wrote:
> > 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.
> >
> > Signed-off-by: Sargun Dhillon <[email protected]>
Could you please add:
Suggested-by: Oleg Nesterov <[email protected]>
and add a line like:
"This is based on a patch sent by Oleg (cf. [1]) a while ago."
[1]: Link: https://lore.kernel.org/r/[email protected]
apart from a few nits below:
Acked-by: Christian Brauner <[email protected]>
> > ---
> > 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..0ceeb046f4f3 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 +729,11 @@ static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
> > return file;
> > }
> >
> > +static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
This can be:
static inline struct file *__fget(...)
> > +{
> > + 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 +751,19 @@ 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);
>
> Nit: remove the \n:
>
> task_lock(task);
> if (task->files)
> file = __fget_files(task->files, fd, 0, 1);
> task_unlock(task);
>
> Christian