linux-kernel - [PATCH] fs: add the FIGETFROZEN ioctl call

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Date:	Thu, 14 Apr 2016 09:57:07 +0200
From:	Florian Margaine <florian@...gaine.com>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	Jeff Layton <jlayton@...chiereds.net>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] fs: add the FIGETFROZEN ioctl call

This lets userland get the filesystem freezing status, aka whether the
filesystem is frozen or not. This is so that an application can know if
it should freeze the filesystem or if it isn't necessary when taking a
snapshot.
---
 fs/compat_ioctl.c       |  1 +
 fs/ioctl.c              | 13 +++++++++++++
 include/uapi/linux/fs.h |  1 +
 3 files changed, 15 insertions(+)

diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
index bd01b92..d2173ab 100644
--- a/fs/compat_ioctl.c
+++ b/fs/compat_ioctl.c
@@ -918,6 +918,7 @@ COMPATIBLE_IOCTL(FIGETBSZ)
 COMPATIBLE_IOCTL(FIFREEZE)
 COMPATIBLE_IOCTL(FITHAW)
 COMPATIBLE_IOCTL(FITRIM)
+COMPATIBLE_IOCTL(FIGETFROZEN)
 COMPATIBLE_IOCTL(KDGETKEYCODE)
 COMPATIBLE_IOCTL(KDSETKEYCODE)
 COMPATIBLE_IOCTL(KDGKBTYPE)
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 116a333..249ed20 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -568,6 +568,16 @@ static int ioctl_fsthaw(struct file *filp)
  return thaw_super(sb);
 }

+static int ioctl_fsgetfrozen(struct file *filp)
+{
+ struct super_block *sb = file_inode(filp)->i_sb;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ return sb->s_writers.frozen;
+}
+
 static long ioctl_file_dedupe_range(struct file *file, void __user *arg)
 {
  struct file_dedupe_range __user *argp = arg;
@@ -652,6 +662,9 @@ int do_vfs_ioctl(struct file *filp, unsigned int
fd, unsigned int cmd,
  error = ioctl_fsthaw(filp);
  break;

+ case FIGETFROZEN:
+ return put_user(ioctl_fsgetfrozen(filp), argp);
+
  case FS_IOC_FIEMAP:
  return ioctl_fiemap(filp, arg);

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 149bec8..d48f19c 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -230,6 +230,7 @@ struct fsxattr {
 #define FIFREEZE _IOWR('X', 119, int) /* Freeze */
 #define FITHAW _IOWR('X', 120, int) /* Thaw */
 #define FITRIM _IOWR('X', 121, struct fstrim_range) /* Trim */
+#define FIGETFROZEN _IOWR('X', 122, int) /* Frozen status */
 #define FICLONE _IOW(0x94, 9, int)
 #define FICLONERANGE _IOW(0x94, 13, struct file_clone_range)
 #define FIDEDUPERANGE _IOWR(0x94, 54, struct file_dedupe_range)
-- 
2.8.0