Makefile / racy-git.txt: clarify USE_NSEC prerequisites
Subsystems (2)
PATCH 1/1 Makefile / racy-git.txt: clarify USE_NSEC prerequisites
Signed-off-by Karsten Blees <[email protected]>
---
Enabling nanosecond file times was recently discussed on the libgit2 project, so I thought its time to fix the nanosecond issue on Linux. Don't know yet if the patch will be accepted (and in which kernel version).
Considering that nanosecond file times are still broken for some file systems, it may be desirable to make this a config option in addition to the compile-time setting? I.e. only use sub-second file times for up-to-date checks if the config option is enabled, so that it can be turned off on file systems with flaky timestamps.
Documentation/technical/racy-git.txt | 8 ++++++-- Makefile | 9 +++++---- 2 files changed, 11 insertions(+), 6 deletions(-)
Documentation/technical/racy-git.txt +6 -2
@@ -42,12 +42,16 @@ compared, but this is not enabled by default because this member is not stable on network filesystems. With `USE_NSEC` compile-time option, `st_mtim.tv_nsec` and `st_ctim.tv_nsec` members are also compared, but this is not enabled by default -because in-core timestamps can have finer granularity than +because on Linux, in-core timestamps can have finer granularity than on-disk timestamps, resulting in meaningless changes when an inode is evicted from the inode cache. See commit 8ce13b0 of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git ([PATCH] Sync in core time granularity with filesystems, -2005-01-04). +2005-01-04). This patch is included in kernel 2.6.11 and newer, but +only fixes the issue for file systems with exactly 1 ns or 1 s +resolution. Other file systems are still broken in current Linux +kernels (e.g. CEPH, CIFS, NTFS, UDF), see +https://lkml.org/lkml/2015/6/9/714 Racy Git --------
Makefile +5 -4
@@ -217,10 +217,11 @@ all:: # as the compiler can crash (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49299) # # Define USE_NSEC below if you want git to care about sub-second file mtimes -# and ctimes. Note that you need recent glibc (at least 2.2.4) for this, and -# it will BREAK YOUR LOCAL DIFFS! show-diff and anything using it will likely -# randomly break unless your underlying filesystem supports those sub-second -# times (my ext3 doesn't). +# and ctimes. Note that you need recent glibc (at least 2.2.4) for this. On +# Linux, kernel 2.6.11 or newer is required for reliable sub-second file times +# on file systems with exactly 1 ns or 1 s resolution. If you intend to use Git +# on other file systems (e.g. CEPH, CIFS, NTFS, UDF), don't enable USE_NSEC. See +# Documentation/technical/racy-git.txt for details. # # Define USE_ST_TIMESPEC if your "struct stat" uses "st_ctimespec" instead of # "st_ctim"
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2.4.3.windows.1.1.g87477f9
Documentation/technical/racy-git.txt compared, but this is not enabled by default because this member · line 50
Quoted 8 lines · Karsten Blees
members are also compared, but this is not enabled by default
Documentation/technical/racy-git.txt +1
-2-because in-core timestamps can have finer granularity than +because on Linux, in-core timestamps can have finer granularity than on-disk timestamps, resulting in meaningless changes when an inode is evicted from the inode cache. See commit 8ce13b0 of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git ([PATCH] Sync in core time granularity with filesystems, -2005-01-04).
Hmm, the above makes one wonder if on systems other than Linux it may be better enabled by default. Perhaps
members are also compared. On Linux, this is not enabled by default because ...
would make the logic and text flow better?
Makefile all:: · line 224
Quoted 10 lines
# Define
USE_NSECbelow if you want git to care about sub-second file mtimesMakefile +5
-4-# and ctimes. Note that you need recent glibc (at least 2.2.4) for this, and -# it will BREAK YOUR LOCAL DIFFS! show-diff and anything using it will likely -# randomly break unless your underlying filesystem supports those sub-second -# times (my ext3 doesn't). +# and ctimes. Note that you need recent glibc (at least 2.2.4) for this. On +# Linux, kernel 2.6.11 or newer is required for reliable sub-second file times +# on file systems with exactly 1 ns or 1 s resolution. If you intend to use Git +# on other file systems (e.g. CEPH, CIFS, NTFS, UDF), don't enable USE_NSEC. See +# Documentation/technical/racy-git.txt for details.
This looks good.
PATCH v2 1/1 Makefile / racy-git.txt: clarify USE_NSEC prerequisites
Signed-off-by Karsten Blees <[email protected]>
---
...just changed wording as you suggested.
Documentation/technical/racy-git.txt | 8 ++++++-- Makefile | 9 +++++---- 2 files changed, 11 insertions(+), 6 deletions(-)
Documentation/technical/racy-git.txt +6 -2
@@ -41,13 +41,17 @@ With a `USE_STDEV` compile-time option, `st_dev` is also compared, but this is not enabled by default because this member is not stable on network filesystems. With `USE_NSEC` compile-time option, `st_mtim.tv_nsec` and `st_ctim.tv_nsec` -members are also compared, but this is not enabled by default +members are also compared. On Linux, this is not enabled by default because in-core timestamps can have finer granularity than on-disk timestamps, resulting in meaningless changes when an inode is evicted from the inode cache. See commit 8ce13b0 of git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git ([PATCH] Sync in core time granularity with filesystems, -2005-01-04). +2005-01-04). This patch is included in kernel 2.6.11 and newer, but +only fixes the issue for file systems with exactly 1 ns or 1 s +resolution. Other file systems are still broken in current Linux +kernels (e.g. CEPH, CIFS, NTFS, UDF), see +https://lkml.org/lkml/2015/6/9/714 Racy Git --------
Makefile +5 -4
@@ -217,10 +217,11 @@ all:: # as the compiler can crash (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49299) # # Define USE_NSEC below if you want git to care about sub-second file mtimes -# and ctimes. Note that you need recent glibc (at least 2.2.4) for this, and -# it will BREAK YOUR LOCAL DIFFS! show-diff and anything using it will likely -# randomly break unless your underlying filesystem supports those sub-second -# times (my ext3 doesn't). +# and ctimes. Note that you need recent glibc (at least 2.2.4) for this. On +# Linux, kernel 2.6.11 or newer is required for reliable sub-second file times +# on file systems with exactly 1 ns or 1 s resolution. If you intend to use Git +# on other file systems (e.g. CEPH, CIFS, NTFS, UDF), don't enable USE_NSEC. See +# Documentation/technical/racy-git.txt for details. # # Define USE_ST_TIMESPEC if your "struct stat" uses "st_ctimespec" instead of # "st_ctim"
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