Re* 2.54.0-rc1 NO_WRITEV=Nope does not work

From

Junio C Hamano <gitster@pobox.com>

Date

Apr 9, 2026, 21:53 UTC

Message-ID

<xmqqmrzbreav.fsf_-_@gitster.g>

In-Reply-To

<20260409211049.GA3119065@coredump.intra.peff.net>

Jeff King <peff@peff.net> writes:

> so you are probably hitting that EINVAL! Which is trying to emulate how
> a system writev() would work, but the fundamental problem is that it
> _doesn't_ work on your system, because ssize_t is too small for how
> we're using writev(), which assumes we can pass in 64k at a time.

Sigh.

> It is tempting to just delete the EINVAL check shown above, but then the
> rest of the fallback function needs to be more clever, and return a
> partial write before incrementing total_written over the ssize_t limit
> (otherwise we have no way to report to the caller how much was actually
> written).
>
> Yuck. I think for 2.54 we either have to truly implement MAX_IO_SIZE
> support, or we have to revert the use of writev() in send_sideband()
> until we do.

Sigh again.

----- >8 -----
Subject: writev: retract the topic until we have a better emulation

Let's revert them and reboot the effort after the release.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Makefile                            |  4 ----
 compat/posix.h                      | 14 ------------
 compat/writev.c                     | 44 -------------------------------------
 config.mak.uname                    |  2 --
 contrib/buildsystems/CMakeLists.txt |  6 +----
 meson.build                         |  1 -
 sideband.c                          | 14 +++---------
 wrapper.c                           | 41 ----------------------------------
 wrapper.h                           |  9 --------
 write-or-die.c                      |  8 -------
 write-or-die.h                      |  1 -
 11 files changed, 4 insertions(+), 140 deletions(-)

diff --git a/Makefile b/Makefile
index 5d22394c2e..cedc234173 100644
--- a/Makefile
+++ b/Makefile
@@ -2029,10 +2029,6 @@ ifdef NO_PREAD
 	COMPAT_CFLAGS += -DNO_PREAD
 	COMPAT_OBJS += compat/pread.o
 endif
-ifdef NO_WRITEV
-	COMPAT_CFLAGS += -DNO_WRITEV
-	COMPAT_OBJS += compat/writev.o
-endif
 ifdef NO_FAST_WORKING_DIRECTORY
 	BASIC_CFLAGS += -DNO_FAST_WORKING_DIRECTORY
 endif
diff --git a/compat/posix.h b/compat/posix.h
index 94699a03fa..faaae1b655 100644
--- a/compat/posix.h
+++ b/compat/posix.h
@@ -137,9 +137,6 @@
 #include <sys/socket.h>
 #include <sys/ioctl.h>
 #include <sys/statvfs.h>
-#ifndef NO_WRITEV
-#include <sys/uio.h>
-#endif
 #include <termios.h>
 #ifndef NO_SYS_SELECT_H
 #include <sys/select.h>
@@ -326,17 +323,6 @@ int git_lstat(const char *, struct stat *);
 ssize_t git_pread(int fd, void *buf, size_t count, off_t offset);
 #endif
 
-#ifdef NO_WRITEV
-#define writev git_writev
-#define iovec git_iovec
-struct git_iovec {
-	void *iov_base;
-	size_t iov_len;
-};
-
-ssize_t git_writev(int fd, const struct iovec *iov, int iovcnt);
-#endif
-
 #ifdef NO_SETENV
 #define setenv gitsetenv
 int gitsetenv(const char *, const char *, int);
diff --git a/compat/writev.c b/compat/writev.c
deleted file mode 100644
index 3a94870a2f..0000000000
--- a/compat/writev.c
+++ /dev/null
@@ -1,44 +0,0 @@
-#include "../git-compat-util.h"
-#include "../wrapper.h"
-
-ssize_t git_writev(int fd, const struct iovec *iov, int iovcnt)
-{
-	size_t total_written = 0;
-	size_t sum = 0;
-
-	/*
-	 * According to writev(3p), the syscall shall error with EINVAL in case
-	 * the sum of `iov_len` overflows `ssize_t`.
-	 */
-	 for (int i = 0; i < iovcnt; i++) {
-		if (iov[i].iov_len > maximum_signed_value_of_type(ssize_t) ||
-		    iov[i].iov_len + sum > maximum_signed_value_of_type(ssize_t)) {
-			errno = EINVAL;
-			return -1;
-		}
-
-		sum += iov[i].iov_len;
-	}
-
-	for (int i = 0; i < iovcnt; i++) {
-		const char *bytes = iov[i].iov_base;
-		size_t iovec_written = 0;
-
-		while (iovec_written < iov[i].iov_len) {
-			ssize_t bytes_written = xwrite(fd, bytes + iovec_written,
-						       iov[i].iov_len - iovec_written);
-			if (bytes_written < 0) {
-				if (total_written)
-					goto out;
-				return bytes_written;
-			}
-			if (!bytes_written)
-				goto out;
-			iovec_written += bytes_written;
-			total_written += bytes_written;
-		}
-	}
-
-out:
-	return (ssize_t) total_written;
-}
diff --git a/config.mak.uname b/config.mak.uname
index ccb3f71881..5feb582558 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -459,7 +459,6 @@ ifeq ($(uname_S),Windows)
 	SANE_TOOL_PATH ?= $(msvc_bin_dir_msys)
 	HAVE_ALLOCA_H = YesPlease
 	NO_PREAD = YesPlease
-	NO_WRITEV = YesPlease
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
 	NO_LIBGEN_H = YesPlease
 	NO_POLL = YesPlease
@@ -675,7 +674,6 @@ ifeq ($(uname_S),MINGW)
 	pathsep = ;
 	HAVE_ALLOCA_H = YesPlease
 	NO_PREAD = YesPlease
-	NO_WRITEV = YesPlease
 	NEEDS_CRYPTO_WITH_SSL = YesPlease
 	NO_LIBGEN_H = YesPlease
 	NO_POLL = YesPlease
diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index d7a087e584..81b4306e72 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -376,7 +376,7 @@ endif()
 #function checks
 set(function_checks
 	strcasestr memmem strlcpy strtoimax strtoumax strtoull
-	setenv mkdtemp poll pread memmem writev)
+	setenv mkdtemp poll pread memmem)
 
 #unsetenv,hstrerror are incompatible with windows build
 if(NOT WIN32)
@@ -421,10 +421,6 @@ if(NOT HAVE_MEMMEM)
 	list(APPEND compat_SOURCES compat/memmem.c)
 endif()
 
-if(NOT HAVE_WRITEV)
-	list(APPEND compat_SOURCES compat/writev.c)
-endif()
-
 if(NOT WIN32)
 	if(NOT HAVE_UNSETENV)
 		list(APPEND compat_SOURCES compat/unsetenv.c)
diff --git a/meson.build b/meson.build
index 8309942d18..11488623bf 100644
--- a/meson.build
+++ b/meson.build
@@ -1429,7 +1429,6 @@ checkfuncs = {
   'initgroups' : [],
   'strtoumax' : ['strtoumax.c', 'strtoimax.c'],
   'pread' : ['pread.c'],
-  'writev' : ['writev.c'],
 }
 
 if host_machine.system() == 'windows'
diff --git a/sideband.c b/sideband.c
index 1ed6614eaf..ea7c25211e 100644
--- a/sideband.c
+++ b/sideband.c
@@ -264,7 +264,6 @@ void send_sideband(int fd, int band, const char *data, ssize_t sz, int packet_ma
 	const char *p = data;
 
 	while (sz) {
-		struct iovec iov[2];
 		unsigned n;
 		char hdr[5];
 
@@ -274,19 +273,12 @@ void send_sideband(int fd, int band, const char *data, ssize_t sz, int packet_ma
 		if (0 <= band) {
 			xsnprintf(hdr, sizeof(hdr), "%04x", n + 5);
 			hdr[4] = band;
-			iov[0].iov_base = hdr;
-			iov[0].iov_len = 5;
+			write_or_die(fd, hdr, 5);
 		} else {
 			xsnprintf(hdr, sizeof(hdr), "%04x", n + 4);
-			iov[0].iov_base = hdr;
-			iov[0].iov_len = 4;
+			write_or_die(fd, hdr, 4);
 		}
-
-		iov[1].iov_base = (void *) p;
-		iov[1].iov_len = n;
-
-		writev_or_die(fd, iov, ARRAY_SIZE(iov));
-
+		write_or_die(fd, p, n);
 		p += n;
 		sz -= n;
 	}
diff --git a/wrapper.c b/wrapper.c
index be8fa575e6..16f5a63fbb 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -323,47 +323,6 @@ ssize_t write_in_full(int fd, const void *buf, size_t count)
 	return total;
 }
 
-ssize_t writev_in_full(int fd, struct iovec *iov, int iovcnt)
-{
-	ssize_t total_written = 0;
-
-	while (iovcnt) {
-		ssize_t bytes_written = writev(fd, iov, iovcnt);
-		if (bytes_written < 0) {
-			if (errno == EINTR || errno == EAGAIN)
-				continue;
-			return -1;
-		}
-		if (!bytes_written) {
-			errno = ENOSPC;
-			return -1;
-		}
-
-		total_written += bytes_written;
-
-		/*
-		 * We first need to discard any iovec entities that have been
-		 * fully written.
-		 */
-		while (iovcnt && (size_t)bytes_written >= iov->iov_len) {
-			bytes_written -= iov->iov_len;
-			iov++;
-			iovcnt--;
-		}
-
-		/*
-		 * Finally, we need to adjust the last iovec in case we have
-		 * performed a partial write.
-		 */
-		if (iovcnt && bytes_written) {
-			iov->iov_base = (char *) iov->iov_base + bytes_written;
-			iov->iov_len -= bytes_written;
-		}
-	}
-
-	return total_written;
-}
-
 ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset)
 {
 	char *p = buf;
diff --git a/wrapper.h b/wrapper.h
index 27519b32d1..15ac3bab6e 100644
--- a/wrapper.h
+++ b/wrapper.h
@@ -47,15 +47,6 @@ ssize_t read_in_full(int fd, void *buf, size_t count);
 ssize_t write_in_full(int fd, const void *buf, size_t count);
 ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset);
 
-/*
- * Try to write all iovecs. Returns -1 in case an error occurred with a proper
- * errno set, the number of bytes written otherwise.
- *
- * Note that the iovec will be modified as a result of this call to adjust for
- * partial writes!
- */
-ssize_t writev_in_full(int fd, struct iovec *iov, int iovcnt);
-
 static inline ssize_t write_str_in_full(int fd, const char *str)
 {
 	return write_in_full(fd, str, strlen(str));
diff --git a/write-or-die.c b/write-or-die.c
index 5f522fb728..01a9a51fa2 100644
--- a/write-or-die.c
+++ b/write-or-die.c
@@ -96,14 +96,6 @@ void write_or_die(int fd, const void *buf, size_t count)
 	}
 }
 
-void writev_or_die(int fd, struct iovec *iov, int iovlen)
-{
-	if (writev_in_full(fd, iov, iovlen) < 0) {
-		check_pipe(errno);
-		die_errno("writev error");
-	}
-}
-
 void fwrite_or_die(FILE *f, const void *buf, size_t count)
 {
 	if (fwrite(buf, 1, count, f) != count)
diff --git a/write-or-die.h b/write-or-die.h
index a045bdfaef..ff0408bd84 100644
--- a/write-or-die.h
+++ b/write-or-die.h
@@ -7,7 +7,6 @@ void fprintf_or_die(FILE *, const char *fmt, ...);
 void fwrite_or_die(FILE *f, const void *buf, size_t count);
 void fflush_or_die(FILE *f);
 void write_or_die(int fd, const void *buf, size_t count);
-void writev_or_die(int fd, struct iovec *iov, int iovlen);
 
 /*
  * These values are used to help identify parts of a repository to fsync.