On 2011-07-18, at 11:21 AM, Josef Bacik <josef@xxxxxxxxxx> wrote:
> This just gets us ready to support the SEEK_HOLE and SEEK_DATA flags. Turns out
> using fiemap in things like cp cause more problems than it solves, so lets try
> and give userspace an interface that doesn't suck. We need to match solaris
> here, and the definitions are
>
> *o* If /whence/ is SEEK_HOLE, the offset of the start of the
> next hole greater than or equal to the supplied offset
> is returned. The definition of a hole is provided near
> the end of the DESCRIPTION.
>
> *o* If /whence/ is SEEK_DATA, the file pointer is set to the
> start of the next non-hole file region greater than or
> equal to the supplied offset.
>
> So in the generic case the entire file is data and there is a virtual hole at
> the end. That means we will just return i_size for SEEK_HOLE and will return
> the same offset for SEEK_DATA. This is how Solaris does it so we have to do it
> the same way.
>
> Thanks,
>
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxx>
> ---
> Documentation/filesystems/porting | 9 +++++++
> fs/read_write.c | 44 ++++++++++++++++++++++++++++++++++--
> include/linux/fs.h | 4 ++-
> 3 files changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
> index 6e29954..e24e7e9 100644
> --- a/Documentation/filesystems/porting
> +++ b/Documentation/filesystems/porting
> @@ -407,3 +407,12 @@ a file off.
> a matter of switching from calling get_sb_... to mount_... and changing the
> function type. If you were doing it manually, just switch from setting ->mnt_root
> to some pointer to returning that pointer. On errors return ERR_PTR(...).
> +
> +[mandatory]
> + If you implement your own ->llseek() you must handle SEEK_HOLE and
> +SEEK_DATA. You can hanle this by returning -EINVAL, but it would be nicer to
> +support it in some way. The generic handler assumes that the entire file is
> +data and there is a virtual hole at the end of the file. So if the provided
> +offset is less than i_size and SEEK_DATA is specified, return the same offset.
> +If the above is true for the offset and you are given SEEK_HOLE, return the end
> +of the file. If the offset is i_size or greater return -ENXIO in either case.
Rather than documenting (only) the way to have a "compliant but not useful SEEK_{HOLE,DATA} implementation, it makes sense to document the desired implementation here as well (what is in the commit comment).
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 5520f8a..5907b49 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -64,6 +64,23 @@ generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
> return file->f_pos;
> offset += file->f_pos;
> break;
> + case SEEK_DATA:
> + /*
> + * In the generic case the entire file is data, so as long as
> + * offset isn't at the end of the file then the offset is data.
> + */
> + if (offset >= inode->i_size)
> + return -ENXIO;
> + break;
> + case SEEK_HOLE:
> + /*
> + * There is a virtual hole at the end of the file, so as long as
> + * offset isn't i_size or larger, return i_size.
> + */
> + if (offset >= inode->i_size)
> + return -ENXIO;
> + offset = inode->i_size;
> + break;
> }
>
> if (offset < 0 && !unsigned_offsets(file))
> @@ -128,12 +145,13 @@ EXPORT_SYMBOL(no_llseek);
>
> loff_t default_llseek(struct file *file, loff_t offset, int origin)
> {
> + struct inode *inode = file->f_path.dentry->d_inode;
> loff_t retval;
>
> - mutex_lock(&file->f_dentry->d_inode->i_mutex);
> + mutex_lock(&inode->i_mutex);
> switch (origin) {
> case SEEK_END:
> - offset += i_size_read(file->f_path.dentry->d_inode);
> + offset += i_size_read(inode);
> break;
> case SEEK_CUR:
> if (offset == 0) {
> @@ -141,6 +159,26 @@ loff_t default_llseek(struct file *file, loff_t offset, int origin)
> goto out;
> }
> offset += file->f_pos;
> + break;
> + case SEEK_DATA:
> + /*
> + * In the generic case the entire file is data, so as
> + * long as offset isn't at the end of the file then the
> + * offset is data.
> + */
> + if (offset >= inode->i_size)
> + return -ENXIO;
> + break;
> + case SEEK_HOLE:
> + /*
> + * There is a virtual hole at the end of the file, so
> + * as long as offset isn't i_size or larger, return
> + * i_size.
> + */
> + if (offset >= inode->i_size)
> + return -ENXIO;
> + offset = inode->i_size;
> + break;
> }
> retval = -EINVAL;
> if (offset >= 0 || unsigned_offsets(file)) {
> @@ -151,7 +189,7 @@ loff_t default_llseek(struct file *file, loff_t offset, int origin)
> retval = offset;
> }
> out:
> - mutex_unlock(&file->f_dentry->d_inode->i_mutex);
> + mutex_unlock(&inode->i_mutex);
> return retval;
> }
> EXPORT_SYMBOL(default_llseek);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b5b9792..c9156f3 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -32,7 +32,9 @@
> #define SEEK_SET 0 /* seek relative to beginning of file */
> #define SEEK_CUR 1 /* seek relative to current file position */
> #define SEEK_END 2 /* seek relative to end of file */
> -#define SEEK_MAX SEEK_END
> +#define SEEK_DATA 3 /* seek to the next data */
> +#define SEEK_HOLE 4 /* seek to the next hole */
> +#define SEEK_MAX SEEK_HOLE
>
> struct fstrim_range {
> __u64 start;
> --
> 1.7.5.2
>
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