fdisk: introduce common fdisk_new_context_fd() helper

We do the same thing over and over again and it's a bit ugly, hence
let's unify the code for it at one common place.

src/shared/fdisk-util.c

@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include "fd-util.h"
+#include "fdisk-util.h"
+
+#if HAVE_LIBFDISK
+
+int fdisk_new_context_fd(int fd, bool read_only, struct fdisk_context **ret) {
+        _cleanup_(fdisk_unref_contextp) struct fdisk_context *c = NULL;
+        int r;
+
+        assert(ret);
+
+        if (fd < 0)
+                return -EBADF;
+
+        c = fdisk_new_context();
+        if (!c)
+                return -ENOMEM;
+
+        r = fdisk_assign_device(c, FORMAT_PROC_FD_PATH(fd), read_only);
+        if (r < 0)
+                return r;
+
+        *ret = TAKE_PTR(c);
+        return 0;
+}
+
+#endif

src/shared/fdisk-util.h

@@ -12,4 +12,6 @@ DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(struct fdisk_partition*, fdisk_unref_partition,
 DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(struct fdisk_parttype*, fdisk_unref_parttype, NULL);
 DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(struct fdisk_table*, fdisk_unref_table, NULL);
 
+int fdisk_new_context_fd(int fd, bool read_only, struct fdisk_context **ret);
+
 #endif

src/shared/meson.build

@@ -125,7 +125,6 @@ shared_sources = files(
         'exit-status.h',
         'extension-release.c',
         'extension-release.h',
-        'fdisk-util.h',
         'fdset.c',
         'fdset.h',
         'fileio-label.c',
@@ -493,3 +492,18 @@ libshared = shared_library(
         dependencies : libshared_deps,
         install : true,
         install_dir : rootpkglibdir)
+
+shared_fdisk_sources = files(
+        'fdisk-util.h',
+        'fdisk-util.c',
+)
+
+if get_option('fdisk') != 'false'
+        libshared_fdisk = static_library(
+                'shared-fdisk',
+                shared_fdisk_sources,
+                include_directories : includes,
+                dependencies : [libfdisk],
+                c_args : ['-fvisibility=default'],
+                build_by_default : false)
+endif