On Mar 8, 2024, at 11:03 AM, Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx> wrote: > > Some filesystems support compressed extents which have a larger logical > size than physical, and for those filesystems, it can be useful for > userspace to know how much space those extents actually use. For > instance, the compsize [1] tool for btrfs currently uses btrfs-internal, > root-only ioctl to find the actual disk space used by a file; it would > be better and more useful for this information to require fewer > privileges and to be usable on more filesystems. Therefore, use one of > the padding u64s in the fiemap extent structure to return the actual > physical length; and, for now, return this as equal to the logical > length. Thank you for working on this patch. Note that there was a patch from David Sterba and a lengthy discussion about exactly this functionality several years ago. If you haven't already read the details, it would be useful to do so. I think the thread had mostly come to good conclusions, but the patch never made it into the kernel. https://patchwork.ozlabs.org/project/linux-ext4/patch/4f8d5dc5b51a43efaf16c39398c23a6276e40a30.1386778303.git.dsterba@xxxxxxx/ One of those conclusions was that the kernel should always fill in the fe_physical_length field in the returned extent, and set a flag: #define FIEMAP_EXTENT_PHYS_LENGTH 0x00000010 to indicate to userspace that the physical length field is valid. There should also be a separate flag for extents that are compressed: #define FIEMAP_EXTENT_DATA_COMPRESSED 0x00000040 Rename fe_length to fe_logical_length and #define fe_length fe_logical_length so that it is more clear which field is which in the data structure, but does not break compatibility. I think this patch gets most of this right, except the presence of the flags to indicate the PHYS_LENGTH and DATA_COMPRESSED state in the extent. Cheers, Andreas > [1] https://github.com/kilobyte/compsize > > Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx> > --- > Documentation/filesystems/fiemap.rst | 26 ++++++++++++++++++-------- > fs/ioctl.c | 1 + > include/uapi/linux/fiemap.h | 24 +++++++++++++++++------- > 3 files changed, 36 insertions(+), 15 deletions(-) > > diff --git a/Documentation/filesystems/fiemap.rst b/Documentation/filesystems/fiemap.rst > index 93fc96f760aa..e3e84573b087 100644 > --- a/Documentation/filesystems/fiemap.rst > +++ b/Documentation/filesystems/fiemap.rst > @@ -80,14 +80,24 @@ Each extent is described by a single fiemap_extent structure as > returned in fm_extents:: > > struct fiemap_extent { > - __u64 fe_logical; /* logical offset in bytes for the start of > - * the extent */ > - __u64 fe_physical; /* physical offset in bytes for the start > - * of the extent */ > - __u64 fe_length; /* length in bytes for the extent */ > - __u64 fe_reserved64[2]; > - __u32 fe_flags; /* FIEMAP_EXTENT_* flags for this extent */ > - __u32 fe_reserved[3]; > + /* > + * logical offset in bytes for the start of > + * the extent from the beginning of the file > + */ > + __u64 fe_logical; > + /* > + * physical offset in bytes for the start > + * of the extent from the beginning of the disk > + */ > + __u64 fe_physical; > + /* length in bytes for this extent */ > + __u64 fe_length; > + /* physical length in bytes for this extent */ > + __u64 fe_physical_length; > + __u64 fe_reserved64[1]; > + /* FIEMAP_EXTENT_* flags for this extent */ > + __u32 fe_flags; > + __u32 fe_reserved[3]; > }; > > All offsets and lengths are in bytes and mirror those on disk. It is valid > diff --git a/fs/ioctl.c b/fs/ioctl.c > index 1d5abfdf0f22..f8e5d6dfc62d 100644 > --- a/fs/ioctl.c > +++ b/fs/ioctl.c > @@ -139,6 +139,7 @@ int fiemap_fill_next_extent(struct fiemap_extent_info *fieinfo, u64 logical, > extent.fe_logical = logical; > extent.fe_physical = phys; > extent.fe_length = len; > + extent.fe_physical_length = len; > extent.fe_flags = flags; > > dest += fieinfo->fi_extents_mapped; > diff --git a/include/uapi/linux/fiemap.h b/include/uapi/linux/fiemap.h > index 24ca0c00cae3..fd3c7d380666 100644 > --- a/include/uapi/linux/fiemap.h > +++ b/include/uapi/linux/fiemap.h > @@ -15,13 +15,23 @@ > #include <linux/types.h> > > struct fiemap_extent { > - __u64 fe_logical; /* logical offset in bytes for the start of > - * the extent from the beginning of the file */ > - __u64 fe_physical; /* physical offset in bytes for the start > - * of the extent from the beginning of the disk */ > - __u64 fe_length; /* length in bytes for this extent */ > - __u64 fe_reserved64[2]; > - __u32 fe_flags; /* FIEMAP_EXTENT_* flags for this extent */ > + /* > + * logical offset in bytes for the start of > + * the extent from the beginning of the file > + */ > + __u64 fe_logical; > + /* > + * physical offset in bytes for the start > + * of the extent from the beginning of the disk > + */ > + __u64 fe_physical; > + /* length in bytes for this extent */ > + __u64 fe_length; > + /* physical length in bytes for this extent */ > + __u64 fe_physical_length; > + __u64 fe_reserved64[1]; > + /* FIEMAP_EXTENT_* flags for this extent */ > + __u32 fe_flags; > __u32 fe_reserved[3]; > }; > > -- > 2.44.0 > > Cheers, Andreas
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