Merge pull request #2989 from Rachid-Koucha/patch-8

[mirror_lxc.git] / CODING_STYLE.md

diff --git a/CODING_STYLE.md b/CODING_STYLE.md
index 80d4096d8d0f56d2617f6430070a906294d5f1ad..fb5022c49cd057c586067856f44b3403e297d40f 100644 (file)
--- a/CODING_STYLE.md
+++ b/CODING_STYLE.md
@@ -633,3 +633,152 @@ string.
 Unless you have a valid reason to accept truncation you must check whether
 truncation has occurred, treat it as an error, and handle the error
 appropriately.
+
+## 25) Use `__fallthrough__` in switch statements
+
+If LXC detects that the compiler is new enough it will tell it to check
+`switch` statements for non-documented fallthroughs. Please always place
+a `__fallthrough__` after a `case` which falls through the next one.
+
+```c
+int lxc_attach_run_command(void *payload)
+{
+       int ret = -1;
+       lxc_attach_command_t *cmd = payload;
+
+       ret = execvp(cmd->program, cmd->argv);
+       if (ret < 0) {
+               switch (errno) {
+               case ENOEXEC:
+                       ret = 126;
+                       break;
+               case ENOENT:
+                       ret = 127;
+                       break;
+               }
+       }
+
+       SYSERROR("Failed to exec \"%s\"", cmd->program);
+       return ret;
+}
+```
+
+## 24) Never use `fgets()`
+
+LXC does not allow the use of `fgets()`. Use `getline()` or other methods
+instead.
+
+## 25) Never allocate memory on the stack
+
+This specifically forbids any usage of `alloca()` in the codebase.
+
+## 26) Use cleanup macros supported by `gcc` and `clang`
+
+LXC has switched from manually cleaning up resources to using cleanup macros
+supported by `gcc` and `clang`:
+```c
+__attribute__((__cleanup__(<my-cleanup-function-wrapper>)))
+```
+We do not allow manually cleanups anymore if there are appropriate macros.
+Currently the following macros are supported:
+```c
+/* close file descriptor */
+__do_close_prot_errno
+
+/* free allocated memory */
+__do_free __attribute__((__cleanup__(__auto_free__)))
+
+/* close FILEs */
+__do_fclose __attribute__((__cleanup__(__auto_fclose__)))
+
+/* close DIRs */
+__do_closedir __attribute__((__cleanup__(__auto_closedir__)))
+```
+For example:
+```c
+void remount_all_slave(void)
+{
+       __do_free char *line = NULL;
+       __do_fclose FILE *f = NULL;
+       __do_close_prot_errno int memfd = -EBADF, mntinfo_fd = -EBADF;
+       int ret;
+       ssize_t copied;
+       size_t len = 0;
+
+       mntinfo_fd = open("/proc/self/mountinfo", O_RDONLY | O_CLOEXEC);
+       if (mntinfo_fd < 0) {
+               SYSERROR("Failed to open \"/proc/self/mountinfo\"");
+               return;
+       }
+
+       memfd = memfd_create(".lxc_mountinfo", MFD_CLOEXEC);
+       if (memfd < 0) {
+               char template[] = P_tmpdir "/.lxc_mountinfo_XXXXXX";
+
+               if (errno != ENOSYS) {
+                       SYSERROR("Failed to create temporary in-memory file");
+                       return;
+               }
+
+               memfd = lxc_make_tmpfile(template, true);
+               if (memfd < 0) {
+                       WARN("Failed to create temporary file");
+                       return;
+               }
+       }
+
+again:
+       copied = lxc_sendfile_nointr(memfd, mntinfo_fd, NULL, LXC_SENDFILE_MAX);
+       if (copied < 0) {
+               if (errno == EINTR)
+                       goto again;
+
+               SYSERROR("Failed to copy \"/proc/self/mountinfo\"");
+               return;
+       }
+
+       ret = lseek(memfd, 0, SEEK_SET);
+       if (ret < 0) {
+               SYSERROR("Failed to reset file descriptor offset");
+               return;
+       }
+
+       f = fdopen(memfd, "r");
+       if (!f) {
+               SYSERROR("Failed to open copy of \"/proc/self/mountinfo\" to mark all shared. Continuing");
+               return;
+       }
+
+       /*
+        * After a successful fdopen() memfd will be closed when calling
+        * fclose(f). Calling close(memfd) afterwards is undefined.
+        */
+       move_fd(memfd);
+
+       while (getline(&line, &len, f) != -1) {
+               char *opts, *target;
+
+               target = get_field(line, 4);
+               if (!target)
+                       continue;
+
+               opts = get_field(target, 2);
+               if (!opts)
+                       continue;
+
+               null_endofword(opts);
+               if (!strstr(opts, "shared"))
+                       continue;
+
+               null_endofword(target);
+               ret = mount(NULL, target, NULL, MS_SLAVE, NULL);
+               if (ret < 0) {
+                       SYSERROR("Failed to make \"%s\" MS_SLAVE", target);
+                       ERROR("Continuing...");
+                       continue;
+               }
+               TRACE("Remounted \"%s\" as MS_SLAVE", target);
+       }
+       TRACE("Remounted all mount table entries as MS_SLAVE");
+}
+```