add f_flags to struct statfs(64)

Add a flags field to help glibc implementing statvfs(3) efficiently.

We copy the flag values from glibc, and add a new ST_VALID flag to denote that f_flags is implemented.

Is f_favail important enough to add as well?

Quoted 1 line · Nick Piggin

Is f_favail important enough to add as well?

As Uli if he needs it. Adding real support for it won't be quite as easy as adding f_flags, as the individual filesystems would need to support it.

And those not derived from FFS generally don't
have any different accounting of inodes allocates vs inodes allocated to non-root user. In fact faking up any kind of free inodes values is already difficult enough for modern filesystems.

Add a flags field to help glibc implementing statvfs(3) efficiently.

We copy the flag values from glibc, and add a new ST_VALID flag to denote that f_flags is implemented.

Signed-off-by Christoph Hellwig <[email protected]>

Index: linux-2.6/arch/mips/include/asm/statfs.h
===================================================================

arch/mips/include/asm/statfs.h +8 -4

@@ -33,7 +33,8 @@ struct statfs {
 	/* Linux specials */
 	__kernel_fsid_t	f_fsid;
 	long		f_namelen;
-	long		f_spare[6];
+	long		f_flags;
+	long		f_spare[5];
 };
 
 #if (_MIPS_SIM == _MIPS_SIM_ABI32) || (_MIPS_SIM == _MIPS_SIM_NABI32)

@@ -53,7 +54,8 @@ struct statfs64 {
 	__u64	f_bavail;
 	__kernel_fsid_t f_fsid;
 	__u32	f_namelen;
-	__u32	f_spare[6];
+	__u32	f_flags;
+	__u32	f_spare[5];
 };
 
 #endif /* _MIPS_SIM == _MIPS_SIM_ABI32 */

@@ -73,7 +75,8 @@ struct statfs64 {			/* Same as struct st
 	/* Linux specials */
 	__kernel_fsid_t	f_fsid;
 	long		f_namelen;
-	long		f_spare[6];
+	long		f_flags;
+	long		f_spare[5];
 };
 
 struct compat_statfs64 {

@@ -88,7 +91,8 @@ struct compat_statfs64 {
 	__u64	f_bavail;
 	__kernel_fsid_t f_fsid;
 	__u32	f_namelen;
-	__u32	f_spare[6];
+	__u32	f_flags;
+	__u32	f_spare[5];
 };
 
 #endif /* _MIPS_SIM == _MIPS_SIM_ABI64 */

Index: linux-2.6/arch/s390/include/asm/statfs.h
===================================================================

arch/s390/include/asm/statfs.h +6 -3

@@ -33,7 +33,8 @@ struct statfs {
 	__kernel_fsid_t f_fsid;
 	int  f_namelen;
 	int  f_frsize;
-	int  f_spare[5];
+	int  f_flags;
+	int  f_spare[4];
 };
 
 struct statfs64 {

@@ -47,7 +48,8 @@ struct statfs64 {
 	__kernel_fsid_t f_fsid;
 	int  f_namelen;
 	int  f_frsize;
-	int  f_spare[5];
+	int  f_flags;
+	int  f_spare[4];
 };
 
 struct compat_statfs64 {

@@ -61,7 +63,8 @@ struct compat_statfs64 {
 	__kernel_fsid_t f_fsid;
 	__u32 f_namelen;
 	__u32 f_frsize;
-	__u32 f_spare[5];
+	__u32 f_flags;
+	__u32 f_spare[4];
 };
 
 #endif /* __s390x__ */

Index: linux-2.6/include/asm-generic/statfs.h
===================================================================

include/asm-generic/statfs.h +5 -2

@@ -33,7 +33,8 @@ struct statfs {
 	__kernel_fsid_t f_fsid;
 	__statfs_word f_namelen;
 	__statfs_word f_frsize;
-	__statfs_word f_spare[5];
+	__statfs_word f_flags;
+	__statfs_word f_spare[4];
 };
 
 /*

@@ -55,7 +56,8 @@ struct statfs64 {
 	__kernel_fsid_t f_fsid;
 	__statfs_word f_namelen;
 	__statfs_word f_frsize;
-	__statfs_word f_spare[5];
+	__statfs_word f_flags;
+	__statfs_word f_spare[4];
 } ARCH_PACK_STATFS64;
 
 /* 

@@ -77,6 +79,7 @@ struct compat_statfs64 {
 	__kernel_fsid_t f_fsid;
 	__u32 f_namelen;
 	__u32 f_frsize;
+	__u32 f_flags[5];
 	__u32 f_spare[5];
 } ARCH_PACK_COMPAT_STATFS64;
 

Index: linux-2.6/include/linux/statfs.h
===================================================================

include/linux/statfs.h +23 -2

@@ -2,7 +2,6 @@
 #define _LINUX_STATFS_H
 
 #include <linux/types.h>
-
 #include <asm/statfs.h>
 
 struct kstatfs {

@@ -16,7 +15,29 @@ struct kstatfs {
 	__kernel_fsid_t f_fsid;
 	long f_namelen;
 	long f_frsize;
-	long f_spare[5];
+	long f_flags;
+	long f_spare[4];
 };
 
+/*
+ * Definitions for the flag in f_flag.
+ *
+ * Generally these flags are equivalent to the MS_ flags used in the mount
+ * ABI.  The exception is ST_VALID which has the same value as MS_REMOUNT
+ * which doesn't make any sense for statfs.
+ */
+#define ST_RDONLY	0x0001	/* mount read-only */
+#define ST_NOSUID	0x0002	/* ignore suid and sgid bits */
+#define ST_NODEV	0x0004	/* disallow access to device special files */
+#define ST_NOEXEC	0x0008	/* disallow program execution */
+#define ST_SYNCHRONOUS	0x0010	/* writes are synced at once */
+#define ST_VALID	0x0020	/* f_flags support is implemented */
+#define ST_MANDLOCK	0x0040	/* allow mandatory locks on an FS */
+/* 0x0080 used for ST_WRITE in glibc */
+/* 0x0100 used for ST_APPEND in glibc */
+/* 0x0200 used for ST_IMMUTABLE in glibc */
+#define ST_NOATIME	0x0400	/* do not update access times */
+#define ST_NODIRATIME	0x0800	/* do not update directory access times */
+#define ST_RELATIME	0x1000	/* update atime relative to mtime/ctime */
+
 #endif

Index: linux-2.6/fs/statfs.c
===================================================================

fs/statfs.c +37 -2

@@ -2,11 +2,40 @@
 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/file.h>
+#include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/statfs.h>
 #include <linux/security.h>
 #include <linux/uaccess.h>
 
+static int calculate_f_flags(struct vfsmount *mnt)
+{
+	struct super_block *sb = mnt->mnt_sb;
+	long flags = ST_VALID;
+
+	if (mnt->mnt_flags & MNT_READONLY)
+		flags |= ST_RDONLY;
+	if (mnt->mnt_flags & MNT_NOSUID)
+		flags |= ST_NOSUID;
+	if (mnt->mnt_flags & MNT_NODEV)
+		flags |= ST_NODEV;
+	if (mnt->mnt_flags & MNT_NOEXEC)
+		flags |= ST_NOEXEC;
+	if (mnt->mnt_flags & MNT_NOATIME)
+		flags |= ST_NOATIME;
+	if (mnt->mnt_flags & MNT_NODIRATIME)
+		flags |= ST_NODIRATIME;
+	if (mnt->mnt_flags & MNT_RELATIME)
+		flags |= ST_RELATIME;
+
+	if (sb->s_flags & MS_SYNCHRONOUS)
+		flags |= ST_SYNCHRONOUS;
+	if (sb->s_flags & MS_MANDLOCK)
+		flags |= ST_MANDLOCK;
+
+	return flags;
+}
+
 int statfs_by_dentry(struct dentry *dentry, struct kstatfs *buf)
 {
 	int retval;

@@ -26,7 +55,12 @@ int statfs_by_dentry(struct dentry *dent
 
 int vfs_statfs(struct path *path, struct kstatfs *buf)
 {
-	return statfs_by_dentry(path->dentry, buf);
+	int error;
+
+	error = statfs_by_dentry(path->dentry, buf);
+	if (!error)
+		buf->f_flags = calculate_f_flags(path->mnt);
+	return error;
 }
 EXPORT_SYMBOL(vfs_statfs);
 

@@ -69,6 +103,7 @@ static int do_statfs_native(struct path
 		buf->f_fsid = st.f_fsid;
 		buf->f_namelen = st.f_namelen;
 		buf->f_frsize = st.f_frsize;
+		buf->f_flags = st.f_flags;
 		memset(buf->f_spare, 0, sizeof(buf->f_spare));
 	}
 	return 0;

@@ -96,6 +131,7 @@ static int do_statfs64(struct path *path
 		buf->f_fsid = st.f_fsid;
 		buf->f_namelen = st.f_namelen;
 		buf->f_frsize = st.f_frsize;
+		buf->f_flags = st.f_flags;
 		memset(buf->f_spare, 0, sizeof(buf->f_spare));
 	}
 	return 0;
--

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while we are adding flags to statfs, I wonder if it might be possible to do something to make f_fsid more useful - particularly for nfs-utils.

Add a flags field to help glibc implementing statvfs(3) efficiently.

We copy the flag values from glibc, and add a new ST_VALID flag to denote that f_flags is implemented.

Signed-off-by Christoph Hellwig<[email protected]>

Index: linux-2.6/include/asm-generic/statfs.h
===================================================================

include/asm-generic/statfs.h +4 -2

@@ -33,7 +33,8 @@ struct statfs {
  	__kernel_fsid_t f_fsid;
  	__statfs_word f_namelen;
  	__statfs_word f_frsize;
-	__statfs_word f_spare[5];
+	__statfs_word f_flags;
+	__statfs_word f_spare[4];
  };
 
  /*

@@ -55,7 +56,8 @@ struct statfs64 {
  	__kernel_fsid_t f_fsid;
  	__statfs_word f_namelen;
  	__statfs_word f_frsize;
-	__statfs_word f_spare[5];
+	__statfs_word f_flags;
+	__statfs_word f_spare[4];
  } ARCH_PACK_STATFS64;
 
  /*

include/asm-generic/statfs.h struct compat_statfs64 { · line 84

Quoted 3 lines

include/asm-generic/statfs.h +1 -0

+	__u32 f_flags[5];
 	__u32 f_spare[5];
 } ARCH_PACK_COMPAT_STATFS64;

This is a typo?

We copy the flag values from glibc, and add a new ST_VALID flag to denote that f_flags is implemented.

I would advocate at least an 8-bit magic value, if there is a concern about this field not always being 0-filled on older kernels, or not using any ST_VALID flag at all, if it was always zero-filled in the past.

Did anyone go back and check which kernel versions didn't clear the spare fields (if any)?

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Quoted 4 lines · Andreas Dilger

I would advocate at least an 8-bit magic value, if there is a concern about this field not always being 0-filled on older kernels, or not using any ST_VALID flag at all, if it was always zero-filled in the past.

Did anyone go back and check which kernel versions didn't clear the spare fields (if any)?

Quoted 3 lines · Ulrich Drepper

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Quoted 5 lines · Andreas Dilger

Quoted 4 lines

I would advocate at least an 8-bit magic value, if there is a concern about this field not always being 0-filled on older kernels, or not using any ST_VALID flag at all, if it was always zero-filled in the past.

ST_VALID is required to differentiate between no flags, and flags field unsupported of course.

Quoted 2 lines

spare fields (if any)?

At least from 2.4.0 does memset it. 2.2.26 does not. Can you live with that?

ST_VALID is required to differentiate between no flags, and flags field unsupported of course.

At least from 2.4.0 does memset it. 2.2.26 does not. Can you live with that?

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Quoted 2 lines · Nick Piggin

ST_VALID is required to differentiate between no flags, and flags field unsupported of course.

Not needed if a new syscall would be used.

Quoted 2 lines

At least from 2.4.0 does memset it. 2.2.26 does not. Can you live with that?

We still support building glibc for everything from linux 2.0 on, at least for x86. I really have no idea whether such old kernels are still in use and if yes, whether userland gets updated. I wouldn't have a problem with bumping the minimum required kernel version.

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Quoted 2 lines · Nick Piggin

ST_VALID is required to differentiate between no flags, and flags field unsupported of course.

Not needed if a new syscall would be used.