From hristo at venev.name  Fri Sep 10 14:18:41 2021
From: hristo at venev.name (Hristo Venev)
Date: Fri, 10 Sep 2021 17:18:41 +0300
Subject: [PATCH] cache: Tolerate short writes in print_slot
Message-ID: <20210910141841.2092532-1-hristo@venev.name>

sendfile() can return after a short read/write, so we may need to call
it more than once. Furthermore, not all files support sendfile(), so we
may need to fall back to read/write.

On the read/write path, use write_in_full which deals with short writes.

Signed-off-by: Hristo Venev <hristo at venev.name>
---
 cache.c | 46 ++++++++++++++++++++++++----------------------
 1 file changed, 24 insertions(+), 22 deletions(-)

diff --git a/cache.c b/cache.c
index 55199e8..85cfbd9 100644
--- a/cache.c
+++ b/cache.c
@@ -85,40 +85,42 @@ static int close_slot(struct cache_slot *slot)
 /* Print the content of the active cache slot (but skip the key). */
 static int print_slot(struct cache_slot *slot)
 {
-#ifdef HAVE_LINUX_SENDFILE
-	off_t start_off;
-	int ret;
+	off_t off;
+	ssize_t i;
+
+	off = slot->keylen + 1;
 
-	start_off = slot->keylen + 1;
+#ifdef HAVE_LINUX_SENDFILE
+	off_t size;
+	size = slot->cache_st.st_size;
 
 	do {
-		ret = sendfile(STDOUT_FILENO, slot->cache_fd, &start_off,
-				slot->cache_st.st_size - start_off);
-		if (ret < 0) {
+		i = sendfile(STDOUT_FILENO, slot->cache_fd, &off, size - off);
+		if (i < 0) {
 			if (errno == EAGAIN || errno == EINTR)
 				continue;
+			/* Fall back to read/write on EINVAL */
+			if (errno == EINVAL)
+				break;
 			return errno;
 		}
-		return 0;
+		if (off == size)
+			return 0;
 	} while (1);
-#else
-	ssize_t i, j;
+#endif
 
-	i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
-	if (i != slot->keylen + 1)
+	if (lseek(slot->cache_fd, off, SEEK_SET) != off)
 		return errno;
 
 	do {
-		i = j = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
-		if (i > 0)
-			j = xwrite(STDOUT_FILENO, slot->buf, i);
-	} while (i > 0 && j == i);
-
-	if (i < 0 || j != i)
-		return errno;
-	else
-		return 0;
-#endif
+		i = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
+		if (i < 0)
+			return errno;
+		if (i == 0)
+			return 0;
+		if (write_in_full(STDOUT_FILENO, slot->buf, i) < 0)
+			return errno;
+	} while (1);
 }
 
 /* Check if the slot has expired */
-- 
2.31.1