Expand comments in elf/ldconfig.c (search_dir)

Developers creating development packages must take care
to have their static linker DSO link point to the actual
SONAME file. This allows ldconfig to correctly create
the required links for the SONAME. The behaviour is now
more clearly documented in a code comment added by this
patch.

diff --git a/ChangeLog b/ChangeLog
index 8a6e89e48eb54ad424202499f05e4157a3f36048..39e70e130c1f3a0e3d6990d033c318696961e4c0 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2014-11-29  Carlos O'Donell  <carlos@redhat.com>
+
+       * elf/ldconfig.c (search_dir): Expand comment.
+
 2014-11-29  Joseph Myers  <joseph@codesourcery.com>
 
        * conform/Makefile (linknamespace-symlist-stdlibs-base): New

diff --git a/elf/ldconfig.c b/elf/ldconfig.c
index 4211f4c9cf7dfa17d670d19432030b264e6eb6c5..2d9c780d228cd2d509c74c1f446db4c26e9573dd 100644 (file)
--- a/elf/ldconfig.c
+++ b/elf/ldconfig.c
@@ -893,8 +893,30 @@ search_dir (const struct dir_entry *entry)
       /* A link may just point to itself.  */
       if (is_link)
        {
-         /* If the path the link points to isn't its soname and it is not
-            .so symlink for ld(1) only, we treat it as a normal file.  */
+         /* If the path the link points to isn't its soname or it is not
+            the .so symlink for ld(1), we treat it as a normal file.
+
+            You should always do this:
+
+               libfoo.so -> SONAME -> Arbitrary package-chosen name.
+
+            e.g. libfoo.so -> libfoo.so.1 -> libfooimp.so.9.99.
+            Given a SONAME of libfoo.so.1.
+
+            You should *never* do this:
+
+               libfoo.so -> libfooimp.so.9.99
+
+            If you do, and your SONAME is libfoo.so.1, then libfoo.so
+            fails to point at the SONAME. In that case ldconfig may consider
+            libfoo.so as another implementation of SONAME and will create
+            symlinks against it causing problems when you try to upgrade
+            or downgrade. The problems will arise because ldconfig will,
+            depending on directory ordering, creat symlinks against libfoo.so
+            e.g. libfoo.so.1.2 -> libfoo.so, but when libfoo.so is removed
+            (typically by the removal of a development pacakge not required
+            for the runtime) it will break the libfoo.so.1.2 symlink and the
+            application will fail to start.  */
          const char *real_base_name = basename (real_file_name);
 
          if (strcmp (real_base_name, soname) != 0)