Introduce loop_read_exact helper

Usually when using loop_read(), we want to read the full buffer.
Add a helper that mirrors loop_write(), and returns 0 when full buffer
was read, and an error otherwise.

Use -ENODATA for the short read, to distinguish it from a read error.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/shared/util.h b/src/shared/util.h
index 2de654f4c..d2da3e289 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -432,6 +432,7 @@ int sigaction_many(const struct sigaction *sa, ...);
 int fopen_temporary(const char *path, FILE **_f, char **_temp_path);
 
 ssize_t loop_read(int fd, void *buf, size_t nbytes, bool do_poll);
+int loop_read_exact(int fd, void *buf, size_t nbytes, bool do_poll);
 int loop_write(int fd, const void *buf, size_t nbytes, bool do_poll);
 
 bool is_device_path(const char *path);