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authorLibravatar Jeff King <peff@peff.net>2021-02-26 01:14:35 -0500
committerLibravatar Junio C Hamano <gitster@pobox.com>2021-02-26 14:15:51 -0800
commit2b08101204066cc8221afb9029c07649f67da0a0 (patch)
tree8d33a9f8020d7d788eed442dbd5089d5ff0d0345 /Makefile
parentMerge branch 'tb/ci-run-cocci-with-18.04' into maint (diff)
downloadtgif-2b08101204066cc8221afb9029c07649f67da0a0.tar.xz
Makefile: add OPEN_RETURNS_EINTR knob
On some platforms, open() reportedly returns EINTR when opening regular files and we receive a signal (usually SIGALRM from our progress meter). This shouldn't happen, as open() should be a restartable syscall, and we specify SA_RESTART when setting up the alarm handler. So it may actually be a kernel or libc bug for this to happen. But it has been reported on at least one version of Linux (on a network filesystem): https://lore.kernel.org/git/c8061cce-71e4-17bd-a56a-a5fed93804da@neanderfunk.de/ as well as on macOS starting with Big Sur even on a regular filesystem. We can work around it by retrying open() calls that get EINTR, just as we do for read(), etc. Since we don't ever _want_ to interrupt an open() call, we can get away with just redefining open, rather than insisting all callsites use xopen(). We actually do have an xopen() wrapper already (and it even does this retry, though there's no indication of it being an observed problem back then; it seems simply to have been lifted from xread(), etc). But it is used hardly anywhere, and isn't suitable for general use because it will die() on error. In theory we could combine the two, but it's awkward to do so because of the variable-args interface of open(). This patch adds a Makefile knob for enabling the workaround. It's not enabled by default for any platforms in config.mak.uname yet, as we don't have enough data to decide how common this is (I have not been able to reproduce on either Linux or Big Sur myself). It may be worth enabling preemptively anyway, since the cost is pretty low (if we don't see an EINTR, it's just an extra conditional). However, note that we must not enable this on Windows. It doesn't do anything there, and the macro overrides the existing mingw_open() redirection. I've added a preemptive #undef here in the mingw header (which is processed first) to just quietly disable it (we could also make it an #error, but there is little point in being so aggressive). Reported-by: Aleksey Kliger <alklig@microsoft.com> Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile7
1 files changed, 7 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index 4128b457e1..08aa57f1db 100644
--- a/Makefile
+++ b/Makefile
@@ -22,6 +22,9 @@ all::
# when attempting to read from an fopen'ed directory (or even to fopen
# it at all).
#
+# Define OPEN_RETURNS_EINTR if your open() system call may return EINTR
+# when a signal is received (as opposed to restarting).
+#
# Define NO_OPENSSL environment variable if you do not have OpenSSL.
#
# Define USE_LIBPCRE if you have and want to use libpcre. Various
@@ -1551,6 +1554,10 @@ ifdef FREAD_READS_DIRECTORIES
COMPAT_CFLAGS += -DFREAD_READS_DIRECTORIES
COMPAT_OBJS += compat/fopen.o
endif
+ifdef OPEN_RETURNS_EINTR
+ COMPAT_CFLAGS += -DOPEN_RETURNS_EINTR
+ COMPAT_OBJS += compat/open.o
+endif
ifdef NO_SYMLINK_HEAD
BASIC_CFLAGS += -DNO_SYMLINK_HEAD
endif