linux-ext4 - [PATCHv3 6/6] Documentation: Correct the description of FIEMAP_EXTENT

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Message-Id: <279638c6939b1f6ef3ab32912cb51da1a967cf8e.1582702694.git.riteshh@linux.ibm.com>
Date:   Wed, 26 Feb 2020 15:27:08 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     jack@...e.cz, tytso@....edu, linux-ext4@...r.kernel.org
Cc:     adilger.kernel@...ger.ca, linux-fsdevel@...r.kernel.org,
        darrick.wong@...cle.com, hch@...radead.org, cmaiolino@...hat.com,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: [PATCHv3 6/6] Documentation: Correct the description of FIEMAP_EXTENT_LAST

Currently FIEMAP_EXTENT_LAST is not working consistently across
different filesystem's fiemap implementations and thus this feature
may be broken. So fix the documentation about this flag to meet the
right expectations.

Signed-off-by: Ritesh Harjani <riteshh@...ux.ibm.com>
---
 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..7c5d22511df7 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. But the user must still confirm by trying to map
+past this extent, since different filesystems implement this differently.
 
 * FIEMAP_EXTENT_UNKNOWN
 The location of this extent is currently unknown. This may indicate
-- 
2.21.0