When we open object files, we try to do so with O_NOATIME.
This dates back to 144bde78e9 (Use O_NOATIME when opening
the sha1 files., 2005-04-23), which is an optimization to
avoid creating a bunch of dirty inodes when we're accessing
many objects.  But a few things have changed since then:

  1. In June 2005, git learned about packfiles, which means
     we would do a lot fewer atime updates (rather than one
     per object access, we'd generally get one per packfile).

  2. In late 2006, Linux learned about "relatime", which is
     generally the default on modern installs. So
     performance around atimes updates is a non-issue there
     these days.

     All the world isn't Linux, but as it turns out, Linux
     is the only platform to implement O_NOATIME in the
     first place.

So it's very unlikely that this code is helping anybody
these days.

Helped-by: Jeff King <peff@peff.net>
[jc: took idea and log message from peff]
Signed-off-by: Junio C Hamano <gitster@pobox.com>

A platform might not support open(2) with O_CLOEXEC but may support
telling the same with fcntl(2) to flip FD_CLOEXEC bit on on an open
file descriptor.  It is a fallback that is inherently racy and this
may not be worth doing, though.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

The way we structured the fallback/retry mechanism for opening with
O_NOATIME and O_CLOEXEC meant that if we failed due to lack of
support to open the file with O_NOATIME option (i.e. EINVAL), we
would still try to drop O_CLOEXEC first and retry, and then drop
O_NOATIME.  A platform on which O_NOATIME is defined in the header
without support from the kernel wouldn't have a chance to open with
O_CLOEXEC option due to this code structure.

Arguably, O_CLOEXEC is more important than O_NOATIME, as the latter
is mostly about performance, while the former can affect correctness.

Instead use O_CLOEXEC to open the file, and then use fcntl(2) to set
O_NOATIME on the resulting file descriptor.  open(2) itself does not
cause atime to be updated according to Linus [*1*].

The helper to do the former can be usable in the codepath in
ce_compare_data() that was recently added to open a file descriptor
with O_CLOEXEC; use it while we are at it.

*1* <CA+55aFw83E+zOd+z5h-CA-3NhrLjVr-anL6pubrSWttYx3zu8g@mail.gmail.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

This fixes "convert: add filter.<driver>.process option" (edcc8581) on
Windows.

Consider the case of a file that requires filtering and is present in
branch A but not in branch B. If A is the current HEAD and we checkout B
then the following happens:

1. ce_compare_data() opens the file
2.   index_fd() detects that the file requires to run a clean filter and
     calls index_stream_convert_blob()
4.     index_stream_convert_blob() calls convert_to_git_filter_fd()
5.       convert_to_git_filter_fd() calls apply_filter() which creates a
         new long running filter process (in case it is the first file
         of this kind to be filtered)
6.       The new filter process inherits all file handles. This is the
         default on Linux/OSX and is explicitly defined in the
         `CreateProcessW` call in `mingw.c` on Windows.
7. ce_compare_data() closes the file
8. Git unlinks the file as it is not present in B

The unlink operation does not work on Windows because the filter process
has still an open handle to the file. On Linux/OSX the unlink operation
succeeds but the file descriptors still leak into the child process.

Fix this problem by opening files in read-cache with the O_CLOEXEC flag
to ensure that the file descriptor does not remain open in a newly
spawned process similar to 05d1ed6148 ("mingw: ensure temporary file
handles are not inherited by child processes", 2016-08-22).

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

All processes that the Git main process spawns inherit the open file
descriptors of the main process. These leaked file descriptors can
cause problems.

Use the O_CLOEXEC flag similar to 05d1ed61 to fix the leaked file
descriptors.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

This function is meant to be used when reading from files in the
object store, and the original objective was to avoid smudging atime
of loose object files too often, hence its name.  Because we'll be
extending its role in the next commit to also arrange the file
descriptors they return auto-closed in the child processes, rename
it to lose "noatime" part that is too specific.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Codepaths involved in interacting alternate object store have
been cleaned up.

* jk/alt-odb-cleanup:
  alternates: use fspathcmp to detect duplicates
  sha1_file: always allow relative paths to alternates
  count-objects: report alternates via verbose mode
  fill_sha1_file: write into a strbuf
  alternates: store scratch buffer as strbuf
  fill_sha1_file: write "boring" characters
  alternates: use a separate scratch space
  alternates: encapsulate alt->base munging
  alternates: provide helper for allocating alternate
  alternates: provide helper for adding to alternates list
  link_alt_odb_entry: refactor string handling
  link_alt_odb_entry: handle normalize_path errors
  t5613: clarify "too deep" recursion tests
  t5613: do not chdir in main process
  t5613: whitespace/style cleanups
  t5613: use test_must_fail
  t5613: drop test_valid_repo function
  t5613: drop reachable_via function

Documentation for "git commit" was updated to clarify that "commit
-p <paths>" adds to the current contents of the index to come up
with what to commit.

* nd/commit-p-doc:
  git-commit.txt: clarify --patch mode with pathspec

"git clone" of a local repository can be done at the filesystem
level, but the codepath did not check errors while copying and
adjusting the file that lists alternate object stores.

* jk/clone-copy-alternates-fix:
  clone: detect errors in normalize_path_copy

http.emptyauth configuration is a way to allow an empty username to
pass when attempting to authenticate using mechanisms like
Kerberos.  We took an unspecified (NULL) username and sent ":"
(i.e. no username, no password) to CURLOPT_USERPWD, but did not do
the same when the username is explicitly set to an empty string.

* dt/http-empty-auth:
  http: http.emptyauth should allow empty (not just NULL) usernames