[PATCH 06/15] lockfile.c: make hold_lock_file_for_append preserve meaningful errno

[Ronnie Sahlberg <sahlberg@google.com>]

Update hold_lock_file_for_append and copy_fd to return a meaningful errno
on failure.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
---
 copy.c     | 20 +++++++++++++-------
 lockfile.c |  7 ++++++-
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/copy.c b/copy.c
index a7f58fd..5cb8679 100644
--- a/copy.c
+++ b/copy.c
@@ -9,10 +9,12 @@ int copy_fd(int ifd, int ofd)
 		if (!len)
 			break;
 		if (len < 0) {
-			int read_error = errno;
+			int save_errno = errno;
 			close(ifd);
-			return error("copy-fd: read returned %s",
-				     strerror(read_error));
+			error("copy-fd: read returned %s",
+			      strerror(save_errno));
+			errno = save_errno;
+			return -1;
 		}
 		while (len) {
 			int written = xwrite(ofd, buf, len);
@@ -22,12 +24,16 @@ int copy_fd(int ifd, int ofd)
 			}
 			else if (!written) {
 				close(ifd);
-				return error("copy-fd: write returned 0");
+				error("copy-fd: write returned 0");
+				errno = EAGAIN;
+				return -1;
 			} else {
-				int write_error = errno;
+				int save_errno = errno;
 				close(ifd);
-				return error("copy-fd: write returned %s",
-					     strerror(write_error));
+				error("copy-fd: write returned %s",
+				      strerror(save_errno));
+				errno = save_errno;
+				return -1;
 			}
 		}
 	}
diff --git a/lockfile.c b/lockfile.c
index a921d77..32f4681 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -217,15 +217,20 @@ int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
 	orig_fd = open(path, O_RDONLY);
 	if (orig_fd < 0) {
 		if (errno != ENOENT) {
+			int save_errno = errno;
 			if (flags & LOCK_DIE_ON_ERROR)
 				die("cannot open '%s' for copying", path);
 			close(fd);
-			return error("cannot open '%s' for copying", path);
+			error("cannot open '%s' for copying", path);
+			errno = save_errno;
+			return -1;
 		}
 	} else if (copy_fd(orig_fd, fd)) {
+		int save_errno = errno;
 		if (flags & LOCK_DIE_ON_ERROR)
 			exit(128);
 		close(fd);
+		errno = save_errno;
 		return -1;
 	}
 	return fd;
-- 
2.0.1.508.g763ab16