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, 192 insertions, 0 deletions

diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst
new file mode 100644
index 000000000..cd28dfe91
--- /dev/null
+++ b/Documentation/admin-guide/index.rst
@@ -0,0 +1,192 @@
+=================================================
+The Linux kernel user's and administrator's guide
+=================================================
+
+The following is a collection of user-oriented documents that have been
+added to the kernel over time.  There is, as yet, little overall order or
+organization here — this material was not written to be a single, coherent
+document!  With luck things will improve quickly over time.
+
+General guides to kernel administration
+---------------------------------------
+
+This initial section contains overall information, including the README
+file describing the kernel as a whole, documentation on kernel parameters,
+etc.
+
+.. toctree::
+   :maxdepth: 1
+
+   README
+   devices
+
+   features
+
+A big part of the kernel's administrative interface is the /proc and sysfs
+virtual filesystems; these documents describe how to interact with tem
+
+.. toctree::
+   :maxdepth: 1
+
+   sysfs-rules
+   sysctl/index
+   cputopology
+   abi
+
+Security-related documentation:
+
+.. toctree::
+   :maxdepth: 1
+
+   hw-vuln/index
+   LSM/index
+   perf-security
+
+Booting the kernel
+------------------
+
+.. toctree::
+   :maxdepth: 1
+
+   bootconfig
+   kernel-parameters
+   efi-stub
+   initrd
+
+
+Tracking down and identifying problems
+--------------------------------------
+
+Here is a set of documents aimed at users who are trying to track down
+problems and bugs in particular.
+
+.. toctree::
+   :maxdepth: 1
+
+   reporting-issues
+   reporting-regressions
+   quickly-build-trimmed-linux
+   verify-bugs-and-bisect-regressions
+   bug-hunting
+   bug-bisect
+   tainted-kernels
+   ramoops
+   dynamic-debug-howto
+   init
+   kdump/index
+   perf/index
+   pstore-blk
+   clearing-warn-once
+   kernel-per-CPU-kthreads
+   lockup-watchdogs
+   RAS/index
+   sysrq
+
+
+Core-kernel subsystems
+----------------------
+
+These documents describe core-kernel administration interfaces that are
+likely to be of interest on almost any system.
+
+.. toctree::
+   :maxdepth: 1
+
+   cgroup-v2
+   cgroup-v1/index
+   cpu-isolation
+   cpu-load
+   mm/index
+   module-signing
+   namespaces/index
+   numastat
+   pm/index
+   syscall-user-dispatch
+
+Support for non-native binary formats.  Note that some of these
+documents are ... old ...
+
+.. toctree::
+   :maxdepth: 1
+
+   binfmt-misc
+   java
+   mono
+
+
+Block-layer and filesystem administration
+-----------------------------------------
+
+.. toctree::
+   :maxdepth: 1
+
+   bcache
+   binderfs
+   blockdev/index
+   cifs/index
+   device-mapper/index
+   ext4
+   filesystem-monitoring
+   nfs/index
+   iostats
+   jfs
+   md
+   ufs
+   xfs
+
+Device-specific guides
+----------------------
+
+How to configure your hardware within your Linux system.
+
+.. toctree::
+   :maxdepth: 1
+
+   acpi/index
+   aoe/index
+   auxdisplay/index
+   braille-console
+   btmrvl
+   dell_rbu
+   edid
+   gpio/index
+   hw_random
+   laptops/index
+   lcd-panel-cgram
+   media/index
+   nvme-multipath
+   parport
+   pnp
+   rapidio
+   rtc
+   serial-console
+   svga
+   thermal/index
+   thunderbolt
+   vga-softcursor
+   video-output
+
+Workload analysis
+-----------------
+
+This is the beginning of a section with information of interest to
+application developers and system integrators doing analysis of the
+Linux kernel for safety critical applications. Documents supporting
+analysis of kernel interactions with applications, and key kernel
+subsystems expectations will be found here.
+
+.. toctree::
+   :maxdepth: 1
+
+   workload-tracing
+
+Everything else
+---------------
+
+A few hard-to-categorize and generally obsolete documents.
+
+.. toctree::
+   :maxdepth: 1
+
+   ldm
+   unicode