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Direct IO via the O_DIRECT flag was originally introduced in XFS by
IRIX for database workloads. Its purpose was to allow the database
to bypass the page and buffer caches to prevent unnecessary IO
operations (e.g. readahead) while preventing contention for system
memory between the database and kernel caches.
On Illumos, there is a library function called directio(3C) that
allows user space to provide a hint to the file system that Direct IO
is useful, but the file system is free to ignore it. The semantics
are also entirely a file system decision. Those that do not
implement it return ENOTTY.
Since the semantics were never defined in any standard, O_DIRECT is
implemented such that it conforms to the behavior described in the
Linux open(2) man page as follows.
1. Minimize cache effects of the I/O.
By design the ARC is already scan-resistant which helps mitigate
the need for special O_DIRECT handling. Data which is only
accessed once will be the first to be evicted from the cache.
This behavior is in consistent with Illumos and FreeBSD.
Future performance work may wish to investigate the benefits of
immediately evicting data from the cache which has been read or
written with the O_DIRECT flag. Functionally this behavior is
very similar to applying the 'primarycache=metadata' property
per open file.
2. O_DIRECT _MAY_ impose restrictions on IO alignment and length.
No additional alignment or length restrictions are imposed.
3. O_DIRECT _MAY_ perform unbuffered IO operations directly
between user memory and block device.
No unbuffered IO operations are currently supported. In order
to support features such as transparent compression, encryption,
and checksumming a copy must be made to transform the data.
4. O_DIRECT _MAY_ imply O_DSYNC (XFS).
O_DIRECT does not imply O_DSYNC for ZFS. Callers must provide
O_DSYNC to request synchronous semantics.
5. O_DIRECT _MAY_ disable file locking that serializes IO
operations. Applications should avoid mixing O_DIRECT
and normal IO or mmap(2) IO to the same file. This is
particularly true for overlapping regions.
All I/O in ZFS is locked for correctness and this locking is not
disabled by O_DIRECT. However, concurrently mixing O_DIRECT,
mmap(2), and normal I/O on the same file is not recommended.
This change is implemented by layering the aops->direct_IO operations
on the existing AIO operations. Code already existed in ZFS on Linux
for bypassing the page cache when O_DIRECT is specified.
References:
* http://xfs.org/docs/xfsdocs-xml-dev/XFS_User_Guide/tmp/en-US/html/ch02s09.html
* https://blogs.oracle.com/roch/entry/zfs_and_directio
* https://ext4.wiki.kernel.org/index.php/Clarifying_Direct_IO's_Semantics
* https://illumos.org/man/3c/directio
Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #224
Closes #7823
224 lines
5.0 KiB
Bash
Executable File
224 lines
5.0 KiB
Bash
Executable File
#!/bin/bash
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REF="HEAD"
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# test a url
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function test_url()
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{
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url="$1"
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if ! curl --output /dev/null --max-time 60 \
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--silent --head --fail "$url" ; then
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echo "\"$url\" is unreachable"
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return 1
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fi
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return 0
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}
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# test commit body for length
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# lines containing urls are exempt for the length limit.
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function test_commit_bodylength()
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{
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length="72"
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body=$(git log -n 1 --pretty=%b "$REF" | grep -Ev "http(s)*://" | grep -E -m 1 ".{$((length + 1))}")
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if [ -n "$body" ]; then
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echo "error: commit message body contains line over ${length} characters"
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return 1
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fi
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return 0
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}
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# check for a tagged line
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function check_tagged_line()
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{
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regex='^\s*'"$1"':\s[[:print:]]+\s<[[:graph:]]+>$'
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foundline=$(git log -n 1 "$REF" | grep -E -m 1 "$regex")
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if [ -z "$foundline" ]; then
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echo "error: missing \"$1\""
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return 1
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fi
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return 0
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}
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# check for a tagged line and check that the link is valid
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function check_tagged_line_with_url()
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{
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regex='^\s*'"$1"':\s\K([[:graph:]]+)$'
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foundline=$(git log -n 1 "$REF" | grep -Po "$regex")
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if [ -z "$foundline" ]; then
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echo "error: missing \"$1\""
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return 1
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fi
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OLDIFS=$IFS
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IFS=$'\n'
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for url in $(echo -e "$foundline"); do
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if ! test_url "$url"; then
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return 1
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fi
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done
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IFS=$OLDIFS
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return 0
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}
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# check commit message for a normal commit
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function new_change_commit()
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{
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error=0
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# subject is not longer than 50 characters
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long_subject=$(git log -n 1 --pretty=%s "$REF" | grep -E -m 1 '.{51}')
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if [ -n "$long_subject" ]; then
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echo "error: commit subject over 50 characters"
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error=1
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fi
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# need a signed off by
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if ! check_tagged_line "Signed-off-by" ; then
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error=1
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fi
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# ensure that no lines in the body of the commit are over 72 characters
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if ! test_commit_bodylength ; then
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error=1
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fi
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return $error
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}
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function is_openzfs_port()
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{
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# subject starts with OpenZFS means it's an openzfs port
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subject=$(git log -n 1 --pretty=%s "$REF" | grep -E -m 1 '^OpenZFS')
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if [ -n "$subject" ]; then
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return 0
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fi
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return 1
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}
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function openzfs_port_commit()
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{
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error=0
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# subject starts with OpenZFS dddd
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subject=$(git log -n 1 --pretty=%s "$REF" | grep -E -m 1 '^OpenZFS [[:digit:]]+(, [[:digit:]]+)* - ')
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if [ -z "$subject" ]; then
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echo "error: OpenZFS patch ports must have a subject line that starts with \"OpenZFS dddd - \""
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error=1
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fi
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# need an authored by line
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if ! check_tagged_line "Authored by" ; then
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error=1
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fi
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# need a reviewed by line
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if ! check_tagged_line "Reviewed by" ; then
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error=1
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fi
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# need a approved by line
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if ! check_tagged_line "Approved by" ; then
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error=1
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fi
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# need ported by line
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if ! check_tagged_line "Ported-by" ; then
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error=1
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fi
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# need a url to openzfs commit and it should be valid
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if ! check_tagged_line_with_url "OpenZFS-commit" ; then
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error=1
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fi
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# need a url to illumos issue and it should be valid
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if ! check_tagged_line_with_url "OpenZFS-issue" ; then
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error=1
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fi
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return $error
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}
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function is_coverity_fix()
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{
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# subject starts with Fix coverity defects means it's a coverity fix
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subject=$(git log -n 1 --pretty=%s "$REF" | grep -E -m 1 '^Fix coverity defects')
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if [ -n "$subject" ]; then
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return 0
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fi
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return 1
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}
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function coverity_fix_commit()
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{
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error=0
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# subject starts with Fix coverity defects: CID dddd, dddd...
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subject=$(git log -n 1 --pretty=%s "$REF" |
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grep -E -m 1 'Fix coverity defects: CID [[:digit:]]+(, [[:digit:]]+)*')
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if [ -z "$subject" ]; then
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echo "error: Coverity defect fixes must have a subject line that starts with \"Fix coverity defects: CID dddd\""
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error=1
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fi
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# need a signed off by
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if ! check_tagged_line "Signed-off-by" ; then
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error=1
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fi
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# test each summary line for the proper format
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OLDIFS=$IFS
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IFS=$'\n'
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for line in $(git log -n 1 --pretty=%b "$REF" | grep -E '^CID'); do
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echo "$line" | grep -E '^CID [[:digit:]]+: ([[:graph:]]+|[[:space:]])+ \(([[:upper:]]|\_)+\)' > /dev/null
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# shellcheck disable=SC2181
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if [[ $? -ne 0 ]]; then
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echo "error: commit message has an improperly formatted CID defect line"
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error=1
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fi
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done
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IFS=$OLDIFS
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# ensure that no lines in the body of the commit are over 72 characters
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if ! test_commit_bodylength; then
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error=1
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fi
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return $error
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}
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if [ -n "$1" ]; then
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REF="$1"
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fi
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# if openzfs port, test against that
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if is_openzfs_port; then
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if ! openzfs_port_commit ; then
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exit 1
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else
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exit 0
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fi
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fi
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# if coverity fix, test against that
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if is_coverity_fix; then
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if ! coverity_fix_commit; then
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exit 1
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else
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exit 0
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fi
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fi
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# have a normal commit
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if ! new_change_commit ; then
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exit 1
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fi
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exit 0
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