Re: [PATCH 2/2] add f_flags to struct statfs(64)

[Neil Brown <neilb@suse.de>]

On Sat, 26 Jun 2010 11:35:07 +0200
Christoph Hellwig <hch@lst.de> wrote:

> 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.

Hi Christoph,
 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.

 Currently some filesystems (e.g. VFAT) set f_fsid based on the device that
 the filesystem is mounted from, while others (e.g. ext3) set f_fsid based on
 the filesystem itself (i.e. from the UUID stored in the superblock).

 This makes f_fsid not generally usable to make the filesystem part of a
 filehandle, as we really don't want to based it in the device if at all
 possible.   This is particularly frustrating as for btrfs, f_fsid is the
 only way to differentiate between subvolumes.

 If we could have a flag "ST_FSID_STABLE" (or similar) which indicates that
 the f_fsid is known to be stable across device renames, then I could remove
 some special casing that was recently added to nfs-utils for btrfs (or at
 least deprecate it).

 And if it was acceptable to use a couple more of the 'spares' to provide a
 full 128bit fsid rather than just a 64bit one, that would be even better.
 But I'm not sure it is worth it (64bits is still quite a lot).

Thanks,
NeilBrown

> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Index: linux-2.6/arch/mips/include/asm/statfs.h
> ===================================================================
> --- linux-2.6.orig/arch/mips/include/asm/statfs.h	2010-06-26 09:26:56.000000000 +0200
> +++ linux-2.6/arch/mips/include/asm/statfs.h	2010-06-26 10:00:33.864004297 +0200
> @@ -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
> ===================================================================
> --- linux-2.6.orig/arch/s390/include/asm/statfs.h	2010-06-26 09:26:56.000000000 +0200
> +++ linux-2.6/arch/s390/include/asm/statfs.h	2010-06-26 10:00:33.864004297 +0200
> @@ -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
> ===================================================================
> --- linux-2.6.orig/include/asm-generic/statfs.h	2010-06-26 09:26:56.000000000 +0200
> +++ linux-2.6/include/asm-generic/statfs.h	2010-06-26 10:00:33.868047809 +0200
> @@ -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
> ===================================================================
> --- linux-2.6.orig/include/linux/statfs.h	2010-06-26 09:26:56.000000000 +0200
> +++ linux-2.6/include/linux/statfs.h	2010-06-26 10:19:53.609016448 +0200
> @@ -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
> ===================================================================
> --- linux-2.6.orig/fs/statfs.c	2010-06-26 09:40:08.000000000 +0200
> +++ linux-2.6/fs/statfs.c	2010-06-26 10:24:27.674272979 +0200
> @@ -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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