[Buildroot] [RFC/PATCH 1/1] systemd: fix remount-fs (Andr? Erdmann)

[Eric Limpens]

Hi Andre, list,

 This is a reply to a digest mail, I hope it doesn't break stuff, but
the following fixes an
 issue I ran into so I feel like I should reply with a tested by.

> Date: Wed, 12 Nov 2014 19:01:06 +0100
> From: Andr? Erdmann <dywi at mailerd.de>
> To: buildroot at buildroot.org
> Subject: [Buildroot] [RFC/PATCH 1/1] systemd: fix remount-fs
> Message-ID: <1415815266-21733-1-git-send-email-dywi at mailerd.de>
> Content-Type: text/plain; charset=UTF-8
>
> systemd runs "/bin/mount MOUNTPOINT -o remount" for remounting
> the rootfs (and others like /usr, /proc, ...) [0]. This is supposed
> to remount the rootfs in rw/ro mode depending on /etc/fstab.
>
> busybox' mount -o remount command, however, complety ignores fstab
> and reads the mount options from /proc/mounts only (+ cmdline "-o ...") [1],
> so "mount / -o remount" is a no-op.
>
> This commit adds a patch that causes systemd's remount-fs to pass the
> options from /etc/fstab to the mount command.
>
> References:
> [0] http://cgit.freedesktop.org/systemd/systemd/tree/src/remount-fs/remount-fs.c?id=v217 (line 99)
> [1] http://git.busybox.net/busybox/tree/util-linux/mount.c?h=1_22_stable (line 2133)
>
> Signed-off-by: Andr? Erdmann <dywi at mailerd.de>

Tested-by: Eric Limpens <limpens at gmail.com>

> ---
>
> Notes:
> * selecting BR2_PACKAGE_UTIL_LINUX_MOUNT=y would also fix remounting,
>   but that also requires BR2_PACKAGE_UTIL_LINUX_BINARIES=y...
>
> * passing all options to mount rather than checking for "rw"/ro"
>   (hasmntopt(...,"ro")==NULL) makes remount-fs behave identical
>   regardless of whether util-linux' or busybox' mount is used
>   (remount-fs also remounts /proc etc.)
>
> * a systemd-based buildroot config ignores BR2_TARGET_GENERIC_REMOUNT_ROOTFS_RW
>   This is not changed by this commit, but the rootfs is now always rw unless
>   /etc/fstab gets replaced by a a postbuild script / rootfs overlay.
>
> By the way, I have a script for generating /etc/fstab, which could be useful
> for dealing with remount-ro/rw and systemd-specific mounts (and maybe genimages).
> Tell me if there's any interest in getting this integrated into buildroot.
>
> You can view it here
>   https://gist.github.com/dywisor/62d41835c2dff043f794#file-mkfstab-bash-L17-L96
> (not the latest revision, but sufficient for getting an overview.)
> ---
>  ...t-fs-pass-options-from-fstab-to-bin-mount.patch | 63 ++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
>  create mode 100644 package/systemd/0005-remount-fs-pass-options-from-fstab-to-bin-mount.patch
>
> diff --git a/package/systemd/0005-remount-fs-pass-options-from-fstab-to-bin-mount.patch b/package/systemd/0005-remount-fs-pass-options-from-fstab-to-bin-mount.patch
> new file mode 100644
> index 0000000..c6dc661
> --- /dev/null
> +++ b/package/systemd/0005-remount-fs-pass-options-from-fstab-to-bin-mount.patch
> @@ -0,0 +1,63 @@
> +From 7bc0901a00e78f22f97dbd3f85c7a19d9a78e7a1 Mon Sep 17 00:00:00 2001
> +From: =?UTF-8?q?Andr=C3=A9=20Erdmann?= <dywi at mailerd.de>
> +Date: Wed, 12 Nov 2014 17:45:46 +0100
> +Subject: [PATCH 1/1] remount-fs: pass options from fstab to /bin/mount
> +MIME-Version: 1.0
> +Content-Type: text/plain; charset=UTF-8
> +Content-Transfer-Encoding: 8bit
> +
> +busybox mount -o remount reads the mount options from /proc/mounts (or mtab);
> +Executing "/bin/mount / -o remount" has no effect when /bin/mount is linked
> +to busybox.
> +
> +remount-fs already reads the options from /etc/fstab,
> +so simply pass them to the mount command.
> +
> +Signed-off-by: Andr? Erdmann <dywi at mailerd.de>
> +---
> + src/remount-fs/remount-fs.c | 11 ++++++++++-
> + 1 file changed, 10 insertions(+), 1 deletion(-)
> +
> +diff --git a/src/remount-fs/remount-fs.c b/src/remount-fs/remount-fs.c
> +index cd7cfe7..f63f009 100644
> +--- a/src/remount-fs/remount-fs.c
> ++++ b/src/remount-fs/remount-fs.c
> +@@ -20,6 +20,7 @@
> + ***/
> +
> + #include <unistd.h>
> ++#include <stdlib.h>
> + #include <fcntl.h>
> + #include <errno.h>
> + #include <string.h>
> +@@ -93,18 +94,26 @@ int main(int argc, char *argv[]) {
> +                 }
> +
> +                 if (pid == 0) {
> ++                        char *opts_str;
> +                         const char *arguments[5];
> +                         /* Child */
> +
> ++                        opts_str = strappend("remount,", me->mnt_opts);
> ++                        if (opts_str == NULL) {
> ++                                log_error("Failed to get remount opts");
> ++                                _exit(EXIT_FAILURE);
> ++                        }
> ++
> +                         arguments[0] = "/bin/mount";
> +                         arguments[1] = me->mnt_dir;
> +                         arguments[2] = "-o";
> +-                        arguments[3] = "remount";
> ++                        arguments[3] = opts_str;
> +                         arguments[4] = NULL;
> +
> +                         execv("/bin/mount", (char **) arguments);
> +
> +                         log_error("Failed to execute /bin/mount: %m");
> ++                        free(opts_str);
> +                         _exit(EXIT_FAILURE);
> +                 }
> +
> +--
> +2.1.3
> +
> --
> 2.1.3