On Fri, Feb 28, 2020 at 02:56:59PM +0530, Ritesh Harjani wrote: > Currently FIEMAP_EXTENT_LAST is not working consistently across > different filesystem's fiemap implementations. So add more information > about how else this flag could set in other implementation. > > Also in general, user should not completely rely on this flag as > such since it could return false value for e.g. > when there is a delalloc extent which might get converted during > writeback, immediately after the fiemap calls return. > > Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx> Looks reasonable, Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> --D > --- > Documentation/filesystems/fiemap.txt | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/Documentation/filesystems/fiemap.txt b/Documentation/filesystems/fiemap.txt > index f6d9c99103a4..fedfa9b9dde5 100644 > --- a/Documentation/filesystems/fiemap.txt > +++ b/Documentation/filesystems/fiemap.txt > @@ -71,8 +71,7 @@ allocated is less than would be required to map the requested range, > the maximum number of extents that can be mapped in the fm_extent[] > array will be returned and fm_mapped_extents will be equal to > fm_extent_count. In that case, the last extent in the array will not > -complete the requested range and will not have the FIEMAP_EXTENT_LAST > -flag set (see the next section on extent flags). > +complete the requested range. > > Each extent is described by a single fiemap_extent structure as > returned in fm_extents. > @@ -96,7 +95,7 @@ block size of the file system. With the exception of extents flagged as > FIEMAP_EXTENT_MERGED, adjacent extents will not be merged. > > The fe_flags field contains flags which describe the extent returned. > -A special flag, FIEMAP_EXTENT_LAST is always set on the last extent in > +A special flag, FIEMAP_EXTENT_LAST *may be* set on the last extent in > the file so that the process making fiemap calls can determine when no > more extents are available, without having to call the ioctl again. > > @@ -115,8 +114,9 @@ data. Note that the opposite is not true - it would be valid for > FIEMAP_EXTENT_NOT_ALIGNED to appear alone. > > * FIEMAP_EXTENT_LAST > -This is the last extent in the file. A mapping attempt past this > -extent will return nothing. > +This is generally the last extent in the file. A mapping attempt past this > +extent may return nothing. In some implementations this flag is also set on > +the last dataset queried by the user (via fiemap->fm_length). > > * FIEMAP_EXTENT_UNKNOWN > The location of this extent is currently unknown. This may indicate > -- > 2.21.0 >
