cache: tolerate short writes in print_slot

sendfile() can return after a short read/write, so we may need to call
it more than once. As suggested in the manual page, we fall back to
read/write if sendfile fails with EINVAL or ENOSYS.

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

Signed-off-by: Hristo Venev <hristo@venev.name>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 25 insertions, 20 deletions

diff --git a/cache.c b/cache.c
index 55199e8..1c843ba 100644
--- a/cache.c
+++ b/cache.c
@@ -85,40 +85,45 @@ 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)
 {
+        off_t off;
 #ifdef HAVE_LINUX_SENDFILE
-        off_t start_off;
-        int ret;
+        off_t size;
+#endif
+
+        off = slot->keylen + 1;
 
-        start_off = slot->keylen + 1;
+#ifdef HAVE_LINUX_SENDFILE
+        size = slot->cache_st.st_size;
 
         do {
-                ret = sendfile(STDOUT_FILENO, slot->cache_fd, &start_off,
-                                slot->cache_st.st_size - start_off);
+                ssize_t ret;
+                ret = sendfile(STDOUT_FILENO, slot->cache_fd, &off, size - off);
                 if (ret < 0) {
                         if (errno == EAGAIN || errno == EINTR)
                                 continue;
+                        /* Fall back to read/write on EINVAL or ENOSYS */
+                        if (errno == EINVAL || errno == ENOSYS)
+                                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
+                ssize_t ret;
+                ret = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
+                if (ret < 0)
+                        return errno;
+                if (ret == 0)
+                        return 0;
+                if (write_in_full(STDOUT_FILENO, slot->buf, ret) < 0)
+                        return errno;
+        } while (1);
 }
 
 /* Check if the slot has expired */