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, 10 insertions, 17 deletions

diff --git a/src/libsystemd/sd-id128/sd-id128.c b/src/libsystemd/sd-id128/sd-id128.c
index c876f6e381..f0ffedc38b 100644
--- a/src/libsystemd/sd-id128/sd-id128.c
+++ b/src/libsystemd/sd-id128/sd-id128.c
@@ -108,9 +108,9 @@ _public_ int sd_id128_get_machine(sd_id128_t *ret) {
         static thread_local bool saved_machine_id_valid = false;
         _cleanup_close_ int fd = -1;
         char buf[33];
-        ssize_t k;
         unsigned j;
         sd_id128_t t;
+        int r;
 
         assert_return(ret, -EINVAL);
 
@@ -123,13 +123,9 @@ _public_ int sd_id128_get_machine(sd_id128_t *ret) {
         if (fd < 0)
                 return -errno;
 
-        k = loop_read(fd, buf, 33, false);
-        if (k < 0)
-                return (int) k;
-
-        if (k != 33)
-                return -EIO;
-
+        r = loop_read_exact(fd, buf, 33, false);
+        if (r < 0)
+                return r;
         if (buf[32] !='\n')
                 return -EIO;
 
@@ -157,10 +153,10 @@ _public_ int sd_id128_get_boot(sd_id128_t *ret) {
         static thread_local bool saved_boot_id_valid = false;
         _cleanup_close_ int fd = -1;
         char buf[36];
-        ssize_t k;
         unsigned j;
         sd_id128_t t;
         char *p;
+        int r;
 
         assert_return(ret, -EINVAL);
 
@@ -173,22 +169,19 @@ _public_ int sd_id128_get_boot(sd_id128_t *ret) {
         if (fd < 0)
                 return -errno;
 
-        k = loop_read(fd, buf, 36, false);
-        if (k < 0)
-                return (int) k;
-
-        if (k != 36)
-                return -EIO;
+        r = loop_read_exact(fd, buf, 36, false);
+        if (r < 0)
+                return r;
 
         for (j = 0, p = buf; j < 16; j++) {
                 int a, b;
 
-                if (p >= buf + k - 1)
+                if (p >= buf + 35)
                         return -EIO;
 
                 if (*p == '-') {
                         p++;
-                        if (p >= buf + k - 1)
+                        if (p >= buf + 35)
                                 return -EIO;
                 }