fs: add fget_many() and fput_many()

commit 091141a42e15fe47ada737f3996b317072afcefb upstream.

Some uses cases repeatedly get and put references to the same file, but
the only exposed interface is doing these one at the time. As each of
these entail an atomic inc or dec on a shared structure, that cost can
add up.

Add fget_many(), which works just like fget(), except it takes an
argument for how many references to get on the file. Ditto fput_many(),
which can drop an arbitrary number of references to a file.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/file.c b/fs/file.c
index 090015401c55ea02ffee8d024ceb81e547c1efb0..aec3804bb71e8717b236c9b38c914c69ee6eb896 100644 (file)
--- a/fs/file.c
+++ b/fs/file.c
@@ -691,7 +691,7 @@ void do_close_on_exec(struct files_struct *files)
        spin_unlock(&files->file_lock);
 }
 
-static struct file *__fget(unsigned int fd, fmode_t mask)
+static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
 {
        struct files_struct *files = current->files;
        struct file *file;
@@ -706,7 +706,7 @@ loop:
                 */
                if (file->f_mode & mask)
                        file = NULL;
-               else if (!get_file_rcu(file))
+               else if (!get_file_rcu_many(file, refs))
                        goto loop;
        }
        rcu_read_unlock();
@@ -714,15 +714,20 @@ loop:
        return file;
 }
 
+struct file *fget_many(unsigned int fd, unsigned int refs)
+{
+       return __fget(fd, FMODE_PATH, refs);
+}
+
 struct file *fget(unsigned int fd)
 {
-       return __fget(fd, FMODE_PATH);
+       return __fget(fd, FMODE_PATH, 1);
 }
 EXPORT_SYMBOL(fget);
 
 struct file *fget_raw(unsigned int fd)
 {
-       return __fget(fd, 0);
+       return __fget(fd, 0, 1);
 }
 EXPORT_SYMBOL(fget_raw);
 
@@ -753,7 +758,7 @@ static unsigned long __fget_light(unsigned int fd, fmode_t mask)
                        return 0;
                return (unsigned long)file;
        } else {
-               file = __fget(fd, mask);
+               file = __fget(fd, mask, 1);
                if (!file)
                        return 0;
                return FDPUT_FPUT | (unsigned long)file;

diff --git a/fs/file_table.c b/fs/file_table.c
index ad17e05ebf95f07888b15f2b09a7b37ac89b9710..747bb386b44661fd1945c20ec45814811b1a2c6a 100644 (file)
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -261,9 +261,9 @@ void flush_delayed_fput(void)
 
 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 
-void fput(struct file *file)
+void fput_many(struct file *file, unsigned int refs)
 {
-       if (atomic_long_dec_and_test(&file->f_count)) {
+       if (atomic_long_sub_and_test(refs, &file->f_count)) {
                struct task_struct *task = current;
 
                if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
@@ -282,6 +282,11 @@ void fput(struct file *file)
        }
 }
 
+void fput(struct file *file)
+{
+       fput_many(file, 1);
+}
+
 /*
  * synchronous analog of fput(); for kernel threads that might be needed
  * in some umount() (and thus can't use flush_delayed_fput() without

diff --git a/include/linux/file.h b/include/linux/file.h
index f87d30882a249d8361425fb668b3f71310832256..67f0888abdde3f09ee4d294b4783fd8a50613814 100644 (file)
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -12,6 +12,7 @@
 struct file;
 
 extern void fput(struct file *);
+extern void fput_many(struct file *, unsigned int);
 
 struct file_operations;
 struct vfsmount;
@@ -40,6 +41,7 @@ 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 unsigned long __fdget(unsigned int fd);
 extern unsigned long __fdget_raw(unsigned int fd);

diff --git a/include/linux/fs.h b/include/linux/fs.h
index cdcef9b3bc60add67076a1114d5a2f0b60e184a4..4865c722ded8521313ac531e444273886f3f46a6 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -923,7 +923,9 @@ static inline struct file *get_file(struct file *f)
        atomic_long_inc(&f->f_count);
        return f;
 }
-#define get_file_rcu(x) atomic_long_inc_not_zero(&(x)->f_count)
+#define get_file_rcu_many(x, cnt)      \
+       atomic_long_add_unless(&(x)->f_count, (cnt), 0)
+#define get_file_rcu(x) get_file_rcu_many((x), 1)
 #define fput_atomic(x) atomic_long_add_unless(&(x)->f_count, -1, 1)
 #define file_count(x)  atomic_long_read(&(x)->f_count)