Subject: [PATCH] test-genzeros: avoid raw write(2)

From: Junio C Hamano <[email-masked]>
Date: Wed, 15 Feb 2023 18:56:14 -0800

This test helper feeds 256kB of data at once to a single invocation
of the write(2) system call, which may be too much for some
platforms.

Call our xwrite() wrapper that knows to honor MAX_IO_SIZE limit and
cope with short writes due to EINTR instead, and die a bit more
loudly by calling die_errno() when xwrite() indicates an error.

Reported-by: Randall S. Becker <[email-masked]>
Helped-by: Jeff King <[email-masked]>
Signed-off-by: Junio C Hamano <[email-masked]>
---

    Junio C Hamano <[email-masked]> writes:

    > Jeff King <[email-masked]> writes:
    >
    >> So yeah, this seems like an obvious good fix. Using write_or_die() might
    >> be even better, as it would report errors rather than quietly returning
    >> non-zero.
    >
    > Maybe.  Let me cook up a version with a proposed log message.

    I ended up avoiding write_or_die() primarily because there is
    nothing "Git" about this helper, which is a poor-man's emulation
    of "dd if=/dev/zero".  It felt a bit too much to pull cache.h in
    as dependency for it.

 t/helper/test-genzeros.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/t/helper/test-genzeros.c b/t/helper/test-genzeros.c
index 8ca988d621..47af843b68 100644
--- a/t/helper/test-genzeros.c
+++ b/t/helper/test-genzeros.c
@@ -17,15 +17,16 @@ int cmd__genzeros(int argc, const char **argv)
 
 	/* Writing out individual NUL bytes is slow... */
 	while (count < 0)
-		if (write(1, zeros, ARRAY_SIZE(zeros)) < 0)
-			return -1;
+		if (xwrite(1, zeros, ARRAY_SIZE(zeros)) < 0)
+			die_errno("write error");
 
 	while (count > 0) {
-		n = write(1, zeros, count < ARRAY_SIZE(zeros) ?
-			  count : ARRAY_SIZE(zeros));
+		n = xwrite(1, zeros,
+			   count < ARRAY_SIZE(zeros)
+			   ? count : ARRAY_SIZE(zeros));
 
 		if (n < 0)
-			return -1;
+			die_errno("write error");
 
 		count -= n;
 	}
-- 
2.39.2-501-gd9d677b2d8