Current code relies on the fact that invalid uid/gid as defined by UDF
2.60 3.3.3.1 and 3.3.3.2 coincides with invalid uid/gid as used by the
user namespaces implementation. Since this is only lucky coincidence,
clean this up to avoid future surprises in case user namespaces
implementation changes. Also this is more robust in presence of valid
(from UDF point of view) uids / gids which do not map into current user
namespace.
Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Pull quota, ext2, isofs and udf fixes from Jan Kara:
- two small quota error handling fixes
- two isofs fixes for architectures with signed char
- several udf block number overflow and signedness fixes
- ext2 rework of mount option handling to avoid GFP_KERNEL allocation
with spinlock held
- ... it also contains a patch to implement auditing of responses to
fanotify permission events. That should have been in the fanotify
pull request but I mistakenly merged that patch into a wrong branch
and noticed only now at which point I don't think it's worth rebasing
and redoing.
* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs:
quota: be aware of error from dquot_initialize
quota: fix potential infinite loop
isofs: use unsigned char types consistently
isofs: fix timestamps beyond 2027
udf: Fix some sign-conversion warnings
udf: Fix signed/unsigned format specifiers
udf: Fix 64-bit sign extension issues affecting blocks > 0x7FFFFFFF
udf: Remove some outdate references from documentation
udf: Avoid overflow when session starts at large offset
ext2: Fix possible sleep in atomic during mount option parsing
ext2: Parse mount options into a dedicated structure
audit: Record fanotify access control decisions
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Large (> 1 TiB) UDF filesystems appear subject to several problems when
mounted on 64-bit systems:
* readdir() can fail on a directory containing File Identifiers residing
above 0x7FFFFFFF. This manifests as a 'ls' command failing with EIO.
* FIBMAP on a file block located above 0x7FFFFFFF can return a negative
value. The low 32 bits are correct, but applications that don't mask the
high 32 bits of the result can perform incorrectly.
Per suggestion by Jan Kara, introduce a udf_pblk_t type for representation
of UDF block addresses. Ultimately, all driver functions that manipulate
UDF block addresses should use this type; for now, deployment is limited
to functions with actual or potential sign extension issues.
Changes to udf_readdir() and udf_block_map() address the issues noted
above; other changes address potential similar issues uncovered during
audit of the driver code.
Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Signed-off-by: Jan Kara <jack@suse.cz>
UDF encodes symlinks in a more complex fashion and thus i_size of a
symlink does not match the lenght of a string returned by readlink(2).
This confuses some applications (see bug 191241) and may be considered a
violation of POSIX. Fix the problem by reading the link into page cache
in response to stat(2) call and report the length of the decoded path.
Signed-off-by: Jan Kara <jack@suse.cz>
Commit 9293fcfbc1
("udf: Remove struct ustr as non-needed intermediate storage"),
while getting rid of 'struct ustr', does not take any special care
of 'dstring' fields and effectively use fixed field length instead
of actual string length, encoded in the last byte of the field.
Also, commit 484a10f493
("udf: Merge linux specific translation into CS0 conversion function")
introduced checking of the length of the string being converted,
requiring proper alignment to number of bytes constituing each
character.
The UDF volume identifier is represented as a 32-bytes 'dstring',
and needs to be converted from CS0 to UTF8, while mounting UDF
filesystem. The changes in mentioned commits can in some cases
lead to incorrect handling of volume identifier:
- if the actual string in 'dstring' is of maximal length and
does not have zero bytes separating it from dstring encoded
length in last byte, that last byte may be included in conversion,
thus making incorrect resulting string;
- if the identifier is encoded with 2-bytes characters (compression
code is 16), the length of 31 bytes (32 bytes of field length minus
1 byte of compression code), taken as the string length, is reported
as an incorrect (unaligned) length, and the conversion fails, which
in its turn leads to volume mounting failure.
This patch introduces handling of 'dstring' encoded length field
in udf_CS0toUTF8 function, that is used in all and only cases
when 'dstring' fields are converted. Currently these cases are
processing of Volume Identifier and Volume Set Identifier fields.
The function is also renamed to udf_dstrCS0toUTF8 to distinctly
indicate that it handles 'dstring' input.
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Although 'struct ustr' tries to structurize the data by combining
the string and its length, it doesn't actually make much benefit,
since it saves only one parameter, but introduces an extra copying
of the whole buffer, serving as an intermediate storage. It looks
quite inefficient and not actually needed.
This commit gets rid of the struct ustr by changing the parameters
of some functions appropriately.
Also, it removes using 'dstring' type, since it doesn't make much
sense too.
Just using the occasion, add a 'const' qualifier to udf_get_filename
to make consistent parameters sets.
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Actual name length restriction is 254 bytes, this is used in 'ustr'
structure, and this is what fits into UDF File Ident structures.
And in most cases the constant is used as UDF_NAME_LEN-2.
So, it's better to just modify the constant to make it closer
to reality.
Also, in some cases it's useful to have a separate constant for
the maximum length of file name field in CS0 encoding in UDF File
Ident structures.
Also, remove the unused UDF_PATH_LEN constant.
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Make the desired output length a parameter rather than have it
hard-coded to UDF_NAME_LEN. Although all call sites still have
this length the same, this parameterization will make the function
more universal and also consistent with udf_get_filename.
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Pull UDF fixes and quota cleanups from Jan Kara:
"Several UDF fixes and some minor quota cleanups"
* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs:
udf: Check output buffer length when converting name to CS0
udf: Prevent buffer overrun with multi-byte characters
quota: constify qtree_fmt_operations structures
udf: avoid uninitialized variable use
udf: Fix lost indirect extent block
udf: Factor out code for creating indirect extent
udf: limit the maximum number of indirect extents in a row
udf: limit the maximum number of TD redirections
fs: make quota/dquot.c explicitly non-modular
fs: make quota/netlink.c explicitly non-modular
Factor out code for creating indirect extent from udf_add_aext(). It was
mostly duplicated in two places. Also remove some opencoded versions
of udf_write_aext().
Signed-off-by: Jan Kara <jack@suse.cz>
Symlink reading code does not check whether the resulting path fits into
the page provided by the generic code. This isn't as easy as just
checking the symlink size because of various encoding conversions we
perform on path. So we have to check whether there is still enough space
in the buffer on the fly.
CC: stable@vger.kernel.org
Reported-by: Carl Henrik Lunde <chlunde@ping.uio.no>
Signed-off-by: Jan Kara <jack@suse.cz>
Some UDF media have special inodes (like VAT or metadata partition
inodes) whose link_count is 0. Thus commit 4071b91362 (udf: Properly
detect stale inodes) broke loading these inodes because udf_iget()
started returning -ESTALE for them. Since we still need to properly
detect stale inodes queried by NFS, create two variants of udf_iget() -
one which is used for looking up special inodes (which ignores
link_count == 0) and one which is used for other cases which return
ESTALE when link_count == 0.
Fixes: 4071b91362
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Currently __udf_read_inode() wasn't returning anything and we found out
whether we succeeded reading inode by checking whether inode is bad or
not. udf_iget() returned NULL on failure and inode pointer otherwise.
Make these two functions properly propagate errors up the call stack and
use the return value in callers.
Signed-off-by: Jan Kara <jack@suse.cz>
This patch implements extent caching in case of file reading.
While reading a file, currently, UDF reads metadata serially
which takes a lot of time depending on the number of extents present
in the file. Caching last accessd extent improves metadata read time.
Instead of reading file metadata from start, now we read from
the cached extent.
This patch considerably improves the time spent by CPU in kernel mode.
For example, while reading a 10.9 GB file using dd:
Time before applying patch:
11677022208 bytes (10.9GB) copied, 1529.748921 seconds, 7.3MB/s
real 25m 29.85s
user 0m 12.41s
sys 15m 34.75s
Time after applying patch:
11677022208 bytes (10.9GB) copied, 1469.338231 seconds, 7.6MB/s
real 24m 29.44s
user 0m 15.73s
sys 3m 27.61s
[JK: Fix bh refcounting issues, simplify initialization]
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
Signed-off-by: Bonggil Bak <bgbak@samsung.com>
Signed-off-by: Jan Kara <jack@suse.cz>
The UDF file-system does not need the 's_dirt' superblock flag because it does
not define the 'write_super()' method. This flag was set to 1 in few places and
set to 0 in '->sync_fs()' and was basically useless. Stop using it because it
is on its way out.
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
note re mount options: fmask and dmask are explicitly truncated to 12bit,
UDF_INVALID_MODE just needs to be guaranteed to differ from any such value.
And umask is used only in &= with umode_t, so we ignore other bits anyway.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs:
udf: Cleanup metadata flags handling
udf: Skip mirror metadata FE loading when metadata FE is ok
ext3: Allow quota file use root reservation
udf: Remove web reference from UDF MAINTAINERS entry
quota: Drop path reference on error exit from quotactl
udf: Neaten udf_debug uses
udf: Neaten logging output, use vsprintf extension %pV
udf: Convert printks to pr_<level>
udf: Rename udf_warning to udf_warn
udf: Rename udf_error to udf_err
udf: Promote some debugging messages to udf_error
ext3: Remove the obsolete broken EXT3_IOC32_WAIT_FOR_READONLY.
udf: Add readpages support for udf.
ext3/balloc.c: local functions should be static
ext2: fix the outdated comment in ext2_nfs_get_inode()
ext3: remove deprecated oldalloc
fs/ext3/balloc.c: delete useless initialization
fs/ext2/balloc.c: delete useless initialization
ext3: fix message in ext3_remount for rw-remount case
ext3: Remove i_mutex from ext3_sync_file()
Fix up trivial (printf format cleanup) conflicts in fs/udf/udfdecl.h
It is not necessary to load mirror metadata FE when metadata FE is OK. So try
to read it only the first time udf_get_pblock_meta25() fails to map the block
from metadata FE.
Signed-off-by: Ashish Sangwan <ashishsangwan2@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Use the current logging styles.
Convert a few printks that should have been udf_warn and udf_err.
Coalesce formats. Add #define pr_fmt.
Move an #include "udfdecls.h" above other includes in udftime.c
so pr_fmt works correctly. Strip prefixes from conversions as appropriate.
Reorder logging definitions in udfdecl.h
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Rename udf_warning to udf_warn for consistency with normal logging
uses of pr_warn.
Rename function udf_warning to _udf_warn.
Remove __func__ from uses and move __func__ to a new udf_warn
macro that calls _udf_warn.
Add \n's to uses of udf_warn, remove \n from _udf_warn.
Coalesce formats.
Reviewed-by: NamJae Jeon <linkinjeon@gmail.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Rename udf_error to udf_err for consistency with normal logging
uses of pr_err.
Rename function udf_err to _udf_err.
Remove __func__ from uses and move __func__ to a new udf_err
macro that calls _udf_err.
Some of the udf_error uses had \n terminations, some did not so
standardize \n's to udf_err uses, remove \n from _udf_err function.
Coalesce udf_err formats.
One message prefixed with udf_read_super is now prefixed with
udf_fill_super.
Reviewed-by: NamJae Jeon <linkinjeon@gmail.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jan Kara <jack@suse.cz>
If there is a problem with a scratched disc or loader, it's valuable to know
which error occurred.
Convert some debug messages to udf_error, neaten those messages too.
Add the calculated tag checksum and the read checksum to error message.
Make udf_error a public function and move the logging prototypes together.
Original-patch-by: NamJae Jeon <linkinjeon@gmail.com>
Reviewed-by: NamJae Jeon <linkinjeon@gmail.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jan Kara <jack@suse.cz>
uniqueID handling has been duplicated in three places. Move it into a common
helper. Since we modify an LVID buffer with uniqueID update, we take
sbi->s_alloc_mutex to protect agaist other modifications of the structure.
Signed-off-by: Jan Kara <jack@suse.cz>
udf_update_inode() does not need BKL since on-disk inode modifications are
protected by the buffer lock and reading of values of in-memory inode is
safe without any lock. In some cases we can write inconsistent inode state
to disk but in that case inode will be marked dirty and overwritten later.
Also make unnecessarily global udf_sync_inode() static.
Signed-off-by: Jan Kara <jack@suse.cz>
Add __attribute__((format... to udf_warning.
All arguments matched formats, no other changes necessary.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Quota on UDF is non-functional at least since 2.6.16 (I'm too lazy to
do more archeology) because it does not provide .quota_write and .quota_read
functions and thus quotaon(8) just returns EINVAL. Since nobody complained
for all those years and quota support is not even in UDF standard just nuke
it.
Signed-off-by: Jan Kara <jack@suse.cz>
Convert udf_ioctl to an unlocked_ioctl and push the BKL down into it.
Signed-off-by: John Kacur <jkacur@redhat.com
Signed-off-by: Jan Kara <jack@suse.cz>
generic setattr not longer responsible for quota transfer.
use udf_setattr for all udf's inodes.
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>
This gives the filesystem more information about the writeback that
is happening. Trond requested this for the NFS unstable write handling,
and other filesystems might benefit from this too by beeing able to
distinguish between the different callers in more detail.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We update information in logical volume integrity descriptor after each
allocation (as LVID contains free space, number of directories and files on
disk etc.). If the filesystem is on some phase change media, this leads to its
quick degradation as such media is able to handle only 10000 overwrites or so.
We solve the problem by writing new information into LVID only on umount,
remount-ro and sync. This solves the problem at the price of longer media
inconsistency (previously media became consistent after pdflush flushed dirty
LVID buffer) but that should be acceptable.
Report by and patch written in cooperation with
Rich Coe <Richard.Coe@med.ge.com>.
Signed-off-by: Jan Kara <jack@suse.cz>
Commit 706047a797, "udf: Fix compilation
warnings when UDF debug is on" inadvertently (I assume) enabled
debugging messages by default for UDF. This patch disables them again.
Signed-off-by: Paul Collins <paul@ondioline.org>
Signed-off-by: Jan Kara <jack@suse.cz>
As pointed out by Sergey Vlasov, UDF implements its own version of
the CRC ITU-T V.41. Convert it to use the one in the library.
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Cc: Sergey Vlasov <vsu@altlinux.ru>
Signed-off-by: Jan Kara <jack@suse.cz>
Fix two compilation warnings (and actual bugs in message formatting)
when UDF debugging is turned on.
Signed-off-by: Sebastian Manciulea <manciuleas@yahoo.com>
Signed-off-by: Jan Kara <jack@suse.cz>
This patch implements parsing of metadata partitions and reading of Metadata
File thus allowing to read UDF 2.50 media. Error resilience is implemented
through accessing the Metadata Mirror File in case the data the Metadata File
cannot be read. The patch is based on the original patch by Sebastian Manciulea
<manciuleas@yahoo.com> and Mircea Fedoreanu <mirceaf_spl@yahoo.com>.
Signed-off-by: Sebastian Manciulea <manciuleas@yahoo.com>
Signed-off-by: Mircea Fedoreanu <mirceaf_spl@yahoo.com>
Signed-off-by: Jan Kara <jack@suse.cz>
* kernel_timestamp type was almost unused - only callers of udf_stamp_to_time
and udf_time_to_stamp used it, so let these functions handle endianness
internally and don't clutter code with conversions
* rename udf_stamp_to_time to udf_disk_stamp_to_time
and udf_time_to_stamp to udf_time_to_disk_stamp
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
- translate udf_file_entry_alloc_offset macro into function
- translate udf_ext0_offset macro into function
- add comment about crypticly named fields in struct udf_inode_info
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
- constify internal crc table
- mark udf_crc "in" parameter as const
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
- fix error handling - always zero output variable
- don't zero explicitely fields zeroed by memset
- mark "in" paramater as const
- remove outdated comment
Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Jan Kara
Linus Torvalds
Greg Kroah-Hartman
Steve Magnani
Steve Kenton
Andrew Gabbasov
Al Viro
Namjae Jeon
Artem Bityutskiy
Joe Perches
Namjae Jeon
John Kacur
Dmitry Monakhov
Christoph Hellwig
Pekka Enberg
Paul Collins
Rasmus Rohde
Bob Copeland
Sebastian Manciulea
Marcin Slusarz