eventfd: show the EFD_SEMAPHORE flag in fdinfo

The EFD_SEMAPHORE flag should be displayed in fdinfo,
as different value could affect the behavior of eventfd.

Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Wen Yang <wenyang.linux@foxmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dylan Yudaken <dylany@fb.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Eric Biggers <ebiggers@google.com>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Message-Id: <tencent_05B9CFEFE6B9BC2A9B3A27886A122A7D9205@qq.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 6c06a52..8aa36cd 100644 (file)
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -33,10 +33,10 @@ struct eventfd_ctx {
        /*
         * Every time that a write(2) is performed on an eventfd, the
         * value of the __u64 being written is added to "count" and a
-        * wakeup is performed on "wqh". A read(2) will return the "count"
-        * value to userspace, and will reset "count" to zero. The kernel
-        * side eventfd_signal() also, adds to the "count" counter and
-        * issue a wakeup.
+        * wakeup is performed on "wqh". If EFD_SEMAPHORE flag was not
+        * specified, a read(2) will return the "count" value to userspace,
+        * and will reset "count" to zero. The kernel side eventfd_signal()
+        * also, adds to the "count" counter and issue a wakeup.
         */
        __u64 count;
        unsigned int flags;
@@ -301,6 +301,8 @@ static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
                   (unsigned long long)ctx->count);
        spin_unlock_irq(&ctx->wqh.lock);
        seq_printf(m, "eventfd-id: %d\n", ctx->id);
+       seq_printf(m, "eventfd-semaphore: %d\n",
+                  !!(ctx->flags & EFD_SEMAPHORE));
 }
 #endif