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vfs, fdtable: Add fget_task helper

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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>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200107175927.4558-2-sargun@sargun.me
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
Sargun Dhillon 2020-01-07 09:59:24 -08:00 • committed by Christian Brauner
parent c79f46a282
commit 5e876fb43d
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GPG key ID: 91C61BC06578DCA2
2 changed files with 22 additions and 2 deletions
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2
include/linux/file.h
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@ -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);