netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 57 insertions, 0 deletions

diff --git a/fs/unicode/README.utf8data b/fs/unicode/README.utf8data
new file mode 100644
index 000000000..f75567e28
--- /dev/null
+++ b/fs/unicode/README.utf8data
@@ -0,0 +1,57 @@
+The utf8data.c file in this directory is generated from the Unicode
+Character Database for version 12.1.0 of the Unicode standard.
+
+The full set of files can be found here:
+
+  http://www.unicode.org/Public/12.1.0/ucd/
+
+Individual source links:
+
+  https://www.unicode.org/Public/12.1.0/ucd/CaseFolding.txt
+  https://www.unicode.org/Public/12.1.0/ucd/DerivedAge.txt
+  https://www.unicode.org/Public/12.1.0/ucd/extracted/DerivedCombiningClass.txt
+  https://www.unicode.org/Public/12.1.0/ucd/DerivedCoreProperties.txt
+  https://www.unicode.org/Public/12.1.0/ucd/NormalizationCorrections.txt
+  https://www.unicode.org/Public/12.1.0/ucd/NormalizationTest.txt
+  https://www.unicode.org/Public/12.1.0/ucd/UnicodeData.txt
+
+md5sums (verify by running "md5sum -c README.utf8data"):
+
+  900e76da1d822a160fd6b8c0b1d70094  CaseFolding.txt
+  131256380bff4fea8ad4a851616f2f10  DerivedAge.txt
+  e731a4089b30002144e107e3d6f8d1fa  DerivedCombiningClass.txt
+  a47c9fbd7ff92a9b261ba9831e68778a  DerivedCoreProperties.txt
+  fcab6dad15e440879d92f315978f93d3  NormalizationCorrections.txt
+  f9ff1c55a60decf436100f791b44aa98  NormalizationTest.txt
+  755f6af699f8c8d2d958da411f78f6c6  UnicodeData.txt
+
+sha1sums (verify by running "sha1sum -c README.utf8data"):
+
+  dc9245f6803c4ac99555c361f5052e0b13eb779b  CaseFolding.txt
+  3281104f237184cdb5d869e86eb8573678ada7da  DerivedAge.txt
+  2f5f995ccb96e0fa84b15151b35d5e2681535175  DerivedCombiningClass.txt
+  5b8698a3fcd5018e1987f296b02e2c17e696415e  DerivedCoreProperties.txt
+  cd83935fbc012345d8792d2c704f69497e753835  NormalizationCorrections.txt
+  ea419aae505b337b0d99a83fa83fe58ddff7c19f  NormalizationTest.txt
+  dc973c0fc93d6f09d9ab9f70d1c9f89c447f0526  UnicodeData.txt
+
+
+To update to the newer version of the Unicode standard, the latest
+released version of the UCD can be found here:
+
+  http://www.unicode.org/Public/UCD/latest/
+
+Then, build under fs/unicode/ with REGENERATE_UTF8DATA=1:
+
+	make REGENERATE_UTF8DATA=1 fs/unicode/
+
+After sanity checking the newly generated utf8data.c file (the
+version generated from the 12.1.0 UCD should be 4,109 lines long, and
+have a total size of 324k) and/or comparing it with the older version
+of utf8data.c_shipped, rename it to utf8data.c_shipped.
+
+If you are a kernel developer updating to a newer version of the
+Unicode Character Database, please update this README.utf8data file
+with the version of the UCD that was used, the md5sum and sha1sums of
+the *.txt files, before checking in the new versions of the utf8data.c
+and README.utf8data files.