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-rw-r--r--api/src/README.Symbol_Versions227
1 files changed, 1 insertions, 226 deletions
diff --git a/api/src/README.Symbol_Versions b/api/src/README.Symbol_Versions
index d69c364bb07..d5cdedd826b 100644
--- a/api/src/README.Symbol_Versions
+++ b/api/src/README.Symbol_Versions
@@ -1,228 +1,3 @@
-1. Symbol Versions and SO_NAMEs
-
- In general, adding new APIs to a shared library does not require that
-symbol versions be used or the the SO_NAME be "bumped." These actions
-are usually reserved for when a major change is introduced, e.g. many
-APIs change or a signficant change in the functionality occurs.
-
- Over the normal lifetime of a When a new API is added, the library is
-recompiled, consumers of the new API are able to do so, and existing,
-legacy consumers of the original API continue as before. If by some
-chance an old copy of the library is installed on a system, it's unlikely
-that most applications will be affected. New applications that use the
-new API will incur a run-time error terminate.
-
- Bumping the SO_NAME, i.e. changing the shared lib's file name, e.g.
-from libfoo.so.0 to libfoo.so.1, which also changes the ELF SO_NAME
-attribute inside the file, works a little differently. libfoo.so.0
-contains only the old APIs. libfoo.so.1 contains both the old and new
-APIs. Legacy software that was linked with libfoo.so.0 continues to work
-as libfoo.so.0 is usually left installed on the system. New software that
-uses the new APIs is linked with libfoo.so.1, and works as long as
-long as libfoo.so.1 is installed on the system. Accidentally (re)installing
-libfoo.so.0 doesn't break new software as long as reinstalling doesn't
-erase libfoo.so.1.
-
- Using symbol versions is somewhere in the middle. The shared library
-file remains libfoo.so.0 forever. Legacy APIs may or may not have an
-associated symbol version. New APIs may or may not have an associated
-symbol version either. In general symbol versions are reserved for APIs
-that have changed. Either the function's signature has changed, i.e. the
-return time or the number of paramaters, and/or the parameter types have
-changed. Another reason for using symbol versions on an API is when the
-behaviour or functionality of the API changes dramatically. As with a
-library that doesn't use versioned symbols, old and new applications
-either find or don't find the versioned symbols they need. If the versioned
-symbol doesn't exist in the installed library, the application incurs a
-run-time error and terminates.
-
- GlusterFS wanted to keep tight control over the APIs in libgfapi.
-Originally bumping the SO_NAME was considered, and GlusterFS-3.6.0 was
-released with libgfapi.so.7. Not only was "7" a mistake (it should have
-been "6"), but it was quickly pointed out that many dependent packages
-that use libgfapi would be forced to be recompiled/relinked. Thus no
-packages of 3.6.0 were ever released and 3.6.1 was quickly released with
-libgfapi.so.0, but with symbol versions. There's no strong technical
-reason for either; the APIs have not changed, only new APIs have been
-added. It's merely being done in anticipation that some APIs might change
-sometime in the future.
-
- Enough about that now, let's get into the nitty gritty——
-
-2. Adding new APIs
-
-2.1. Adding a public API.
-
- This is the default, and the easiest thing to do. Public APIs have
-declarations in either glfs.h, glfs-handles.h, or, at your discretion,
-in a new header file intended for consumption by other developers.
-
-Here's what you need to do to add a new public API:
-
-+ Write the declaration, e.g. in glfs.h:
-
- int glfs_dtrt (const char *volname, void *stuff) __THROW
-
-+ Write the definition, e.g. in glfs-dtrt.c:
-
- int
- pub_glfs_dtrt (const char *volname, void *stuff)
- {
- ...
- return 0;
- }
-
-+ Add the symbol version magic for ELF, gnu toolchain to the definition.
-
- following the definition of your new function in glfs-dtrtops.c, add a
- line like this:
-
- GFAPI_SYMVER_PUBLIC_DEFAULT(glfs_dtrt, 3.7.0)
-
- The whole thing should look like:
-
- int
- pub_glfs_dtrt (const char *volname, void *stuff)
- {
- ...
- }
- GFAPI_SYMVER_PUBLIC_DEFAULT(glfs_dtrt, 3.7.0);
-
- In this example, 3.7.0 refers to the Version the symbol will first
- appear in. There's nothing magic about it, it's just a string token.
- The current versions we have are 3.4.0, 3.4.2, 3.5.0, 3.5.1, and 3.6.0.
- They are to be considered locked or closed. You can not, must not add
- any new APIs and use these versions. Most new APIs will use 3.7.0. If
- you add a new API appearing in 3.6.2 (and mainline) then you would use
- 3.6.2.
-
-+ Add the symbol version magic for OS X to the declaration.
-
- following the declaration in glfs.h, add a line like this:
-
- GFAPI_PUBLIC(glfs_dtrt, 3.7.0)
-
- The whole thing should look like:
-
- int glfs_dtrt (const char *volname, void *stuff) __THROW
- GFAPI_PUBLIC(glfs_dtrt, 3.7.0);
-
- The version here must match the version associated with the definition.
-
-+ Add the new API to the ELF, gnu toolchain link map file, gfapi.map
-
- Most new public APIs will probably be added to a new section that
- looks like this:
-
- GFAPI_3.7.0 {
- global:
- glfs_dtrt;
- } GFAPI_PRIVATE_3.7.0;
-
- if you're adding your new API to, e.g. 3.6.2, it'll look like this:
-
- GFAPI_3.6.2 {
- global:
- glfs_dtrt;
- } GFAPI_3.6.0;
-
- and you must change the
- GFAPI_PRIVATE_3.7.0 { ...} GFAPI_3.6.0;
- section to:
- GFAPI_PRIVATE_3.7.0 { ...} GFAPI_3.6.2;
-
-+ Add the new API to the OS X alias list file, gfapi.aliases.
-
- Most new APIs will use a line that looks like this:
-
- _pub_glfs_dtrt _glfs_dtrt$GFAPI_3.7.0
-
- if you're adding your new API to, e.g. 3.6.2, it'll look like this:
-
- _pub_glfs_dtrt _glfs_dtrt$GFAPI_3.6.2
-
-And that's it.
-
-
-2.2. Adding a private API.
-
- If you're thinking about adding a private API that isn't declared in
-one of the header files, then you should seriously rethink what you're
-doing and figure out how to put it in libglusterfs instead.
-
-If that hasn't convinced you, follow the instructions above, but use the
-_PRIVATE versions of macros, symbol versions, and aliases. If you're 1337
-enough to ignore this advice, then you're 1337 enough to figure out how
-to do it.
-
-
-3. Changing an API.
-
-3.1 Changing a public API.
-
- There are two ways an API might change, 1) its signature has changed, or
-2) its new functionality or behavior is substantially different than the
-old. An APIs signature consists of the function return type, and the number
-and/or type of its parameters. E.g. the original API:
-
- int glfs_dtrt (const char *volname, void *stuff);
-
-and the changed API:
-
- void *glfs_dtrt (const char *volname, glfs_t *ctx, void *stuff);
-
- One way to avoid a change like this, and which is preferable in many
-ways, is to leave the legacy glfs_dtrt() function alone, document it as
-deprecated, and simply add a new API, e.g. glfs_dtrt2(). Practically
-speaking, that's effectively what we'll be doing anyway, the difference
-is only that we'll use a versioned symbol to do it.
-
- On the assumption that adding a new API is undesirable for some reason,
-perhaps the use of glfs_gnu() is just so pervasive that we really don't
-want to add glfs_gnu2().
-
-+ change the declaration in glfs.h:
-
- glfs_t *glfs_gnu (const char *volname, void *stuff) __THROW
- GFAPI_PUBLIC(glfs_gnu, 3.7.0);
-
-Note that there is only the single, new declaration.
-
-+ change the old definition of glfs_gnu() in glfs.c:
-
- struct glfs *
- pub_glfs_gnu340 (const char * volname)
- {
- ...
- }
- GFAPI_SYMVER_PUBLIC(glfs_gnu340, glfs_gnu, 3.4.0);
-
-+ create the new definition of glfs_gnu in glfs.c:
-
- struct glfs *
- pub_glfs_gnu (const char * volname, void *stuff)
- {
- ...
- }
- GFAPI_SYMVER_PUBLIC_DEFAULT(glfs_gnu, 3.7.0);
-
-+ Add the new API to the ELF, gnu toolchain link map file, gfapi.map
-
- GFAPI_3.7.0 {
- global:
- glfs_gnu;
- } GFAPI_PRIVATE_3.7.0;
-
-+ Update the OS X alias list file, gfapi.aliases, for both versions:
-
-Change the old line:
- _pub_glfs_gnu _glfs_gnu$GFAPI_3.4.0
-to:
- _pub_glfs_gnu340 _glfs_gnu$GFAPI_3.4.0
-
-Add a new line:
- _pub_glfs_gnu _glfs_gnu$GFAPI_3.7.0
-
-+ Lastly, change all gfapi internal calls glfs_gnu to the new API.
+See .../doc/gfapi-symbol-versions/gfapi-symbol-versions.md