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Re: [PATCH 2/3] statxat: Add a system call to make extended file stats available [ver #2]


On Nov 12, 2013, at 11:41 AM, David Howells <dhowells@redhat.com> wrote:

> Add a system call to make extended file stats available, including file
> creation time, inode version and data version where available through the
> underlying filesystem.

[snip]

> The defined bits in st_ioc_flags are the usual FS_xxx_FL, plus some extra flags
> that might be supplied by the filesystem.  Note that Ext4 returns flags outside
> of {EXT4,FS}_FL_USER_VISIBLE in response to FS_IOC_GETFLAGS.  Should
> {EXT4,FS}_FL_USER_VISIBLE be extended to cover them?  Or should the extra flags
> be suppressed?

This is a bug in the ext4 code.  EXT4_FL_USER_VISIBLE should be extended to cover
all of the flags that are useful to userspace.

> diff --git a/fs/stat.c b/fs/stat.c
> index d0ea7ef75e26..a5e603753bd3 100644
> --- a/fs/stat.c
> +++ b/fs/stat.c
> +/**
> + * vfs_fstatx - Get the enhanced basic attributes by file descriptor
> + * @fd: The file descriptor refering to the file of interest
> + * @stat: The result structure to fill in.
> + *
> + * This function is a wrapper around vfs_xgetattr().  The main difference is
> + * that it uses a file descriptor to determine the file location.
> + *
> + * The caller must have preset stat->query_flags, stat->request_mask and
> + * stat->auxinfo as for vfs_xgetattr().
> + *
> + * 0 will be returned on success, and a -ve error code if unsuccessful.
> + */
> +int vfs_fstatx(unsigned int fd, struct kstat *stat)
> {
> 	struct fd f = fdget_raw(fd);
> 	int error = -EBADF;
> 
> 	if (f.file) {
> -		error = vfs_getattr(&f.file->f_path, stat);
> +		error = vfs_xgetattr(&f.file->f_path, stat);
> 		fdput(f);
> 	}
> 	return error;
> }
> +EXPORT_SYMBOL(vfs_fstatx);
> +
> +/**
> + * vfs_fstat - Get basic attributes by file descriptor
> + * @fd: The file descriptor refering to the file of interest
> + * @stat: The result structure to fill in.
> + *
> + * This function is a wrapper around vfs_getattr().  The main difference is

Typo above - vfs_fstat() is a wrapper around vfs_fstatx().

> + * that it uses a file descriptor to determine the file location.
> + *
> + * 0 will be returned on success, and a -ve error code if unsuccessful.
> + */
> +int vfs_fstat(unsigned int fd, struct kstat *stat)
> +{
> +	stat->query_flags = 0;
> +	stat->request_mask = STATX_BASIC_STATS;
> +	stat->auxinfo = NULL;
> +	return vfs_fstatx(fd, stat);
> +}
> EXPORT_SYMBOL(vfs_fstat);

[snip]

> +/*
> + * Flags to be st_mask
> + *
> + * Query request/result mask for statxat() and struct statx::st_mask.
> + *
> + * These bits should be set in the mask argument of statxat() to request
> + * particular items when calling statxat().
> + */
> +#define STATX_MODE		0x00000001U	/* Want/got st_mode */
> +#define STATX_NLINK		0x00000002U	/* Want/got st_nlink */
> +#define STATX_UID		0x00000004U	/* Want/got st_uid */
> +#define STATX_GID		0x00000008U	/* Want/got st_gid */
> +#define STATX_RDEV		0x00000010U	/* Want/got st_rdev */
> +#define STATX_ATIME		0x00000020U	/* Want/got st_atime */
> +#define STATX_MTIME		0x00000040U	/* Want/got st_mtime */
> +#define STATX_CTIME		0x00000080U	/* Want/got st_ctime */
> +#define STATX_INO		0x00000100U	/* Want/got st_ino */
> +#define STATX_SIZE		0x00000200U	/* Want/got st_size */
> +#define STATX_BLOCKS		0x00000400U	/* Want/got st_blocks */
> +#define STATX_ALLOC_BLKSIZE	0x00000800U	/* Want/got st_alloc_blksize */
> +#define STATX_IO_PARAMS		0x00000800U	/* Want/got I/O parameters */
> +#define STATX_BASIC_STATS	0x00000fffU	/* The stuff in the normal stat struct */

Does it make sense for code clarity to #define STATX_BASIC_STATS explicitly in terms
of the symbolic STATX_* fields, instead of just the numeric value?

> +#define STATX_BTIME		0x00001000U	/* Want/got st_btime */
> +#define STATX_VERSION		0x00002000U	/* Want/got st_version */
> +#define STATX_IOC_FLAGS		0x00004000U	/* Want/got FS_IOC_GETFLAGS */
> +#define STATX_ALL_STATS		0x00007fffU	/* All supported stats */

This could be #defined in terms of STATX_BASIC_STATS | STATX_{other flags} to make
it easier to see what is in the basic flags, and what is extra.

Cheers, Andreas





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