fs: introduce file_getattr and file_setattr syscalls

Introduce file_getattr() and file_setattr() syscalls to manipulate inode
extended attributes. The syscalls takes pair of file descriptor and
pathname. Then it operates on inode opened accroding to openat()
semantics. The struct file_attr is passed to obtain/change extended
attributes.

This is an alternative to FS_IOC_FSSETXATTR ioctl with a difference
that file don't need to be open as we can reference it with a path
instead of fd. By having this we can manipulated inode extended
attributes not only on regular files but also on special ones. This
is not possible with FS_IOC_FSSETXATTR ioctl as with special files
we can not call ioctl() directly on the filesystem inode using fd.

This patch adds two new syscalls which allows userspace to get/set
extended inode attributes on special files by using parent directory
and a path - *at() like syscall.

CC: linux-api@vger.kernel.org
CC: linux-fsdevel@vger.kernel.org
CC: linux-xfs@vger.kernel.org
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
Link: https://lore.kernel.org/20250630-xattrat-syscall-v6-6-c4e3bc35227b@kernel.org
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

3 files changed, 32 insertions, 1 deletions

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index e5603cc91963..77f45e5d4413 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -78,6 +78,7 @@ struct cachestat;
 struct statmount;
 struct mnt_id_req;
 struct xattr_args;
+struct file_attr;
 
 #include <linux/types.h>
 #include <linux/aio_abi.h>
@@ -371,6 +372,12 @@ asmlinkage long sys_removexattrat(int dfd, const char __user *path,
 asmlinkage long sys_lremovexattr(const char __user *path,
 				 const char __user *name);
 asmlinkage long sys_fremovexattr(int fd, const char __user *name);
+asmlinkage long sys_file_getattr(int dfd, const char __user *filename,
+				 struct file_attr __user *attr, size_t usize,
+				 unsigned int at_flags);
+asmlinkage long sys_file_setattr(int dfd, const char __user *filename,
+				 struct file_attr __user *attr, size_t usize,
+				 unsigned int at_flags);
 asmlinkage long sys_getcwd(char __user *buf, unsigned long size);
 asmlinkage long sys_eventfd2(unsigned int count, int flags);
 asmlinkage long sys_epoll_create1(int flags);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 2892a45023af..04e0077fb4c9 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -852,8 +852,14 @@ __SYSCALL(__NR_removexattrat, sys_removexattrat)
 #define __NR_open_tree_attr 467
 __SYSCALL(__NR_open_tree_attr, sys_open_tree_attr)
 
+/* fs/inode.c */
+#define __NR_file_getattr 468
+__SYSCALL(__NR_file_getattr, sys_file_getattr)
+#define __NR_file_setattr 469
+__SYSCALL(__NR_file_setattr, sys_file_setattr)
+
 #undef __NR_syscalls
-#define __NR_syscalls 468
+#define __NR_syscalls 470
 
 /*
  * 32 bit systems traditionally used different
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 0098b0ce8ccb..9663dbdda181 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -149,6 +149,24 @@ struct fsxattr {
 };
 
 /*
+ * Variable size structure for file_[sg]et_attr().
+ *
+ * Note. This is alternative to the structure 'struct fileattr'/'struct fsxattr'.
+ * As this structure is passed to/from userspace with its size, this can
+ * be versioned based on the size.
+ */
+struct file_attr {
+	__u64 fa_xflags;	/* xflags field value (get/set) */
+	__u32 fa_extsize;	/* extsize field value (get/set)*/
+	__u32 fa_nextents;	/* nextents field value (get)   */
+	__u32 fa_projid;	/* project identifier (get/set) */
+	__u32 fa_cowextsize;	/* CoW extsize field value (get/set) */
+};
+
+#define FILE_ATTR_SIZE_VER0 24
+#define FILE_ATTR_SIZE_LATEST FILE_ATTR_SIZE_VER0
+
+/*
  * Flags for the fsx_xflags field
  */
 #define FS_XFLAG_REALTIME	0x00000001	/* data in realtime volume */