[systemd-devel] [PATCH 1/2] fstab-generator: Support root on tmpfs (or other deviceless FS)

[Tobias Hunger]

Hi Tom,

no, root=tmpfs rootfstype=tmpfs does *not* work without my patch. I
had thought it should, too, and I did try.

fstab-generator was silently ignoring root= since "tmpfs" is not a
device. So no mount unit for /sysroot...

Since fstab-generator did evaluate mount.usr* which did point to a
real device it did create a sysroot-usr.mount unit though. So the
initrd did create /sysroot/usr, mounted my usr-subvol there and then
happily switched into the /sysroot directory. At that point systemd
was no longer happy at all and produced lots of funny error messages
about devices being missing.

Best Regards,
Tobias

On Tue, Mar 24, 2015 at 4:39 PM, Tom Gundersen <teg at jklm.no> wrote:
> Hi Tobias and Zbigniew,
>
> This already went in, but I was just looking at it again.
>
> Is there any reason the kernel commandline handling must be treated
> differently here than the fstab handling? We already support
> deviceless mounts (obviously) when specified in fstab without the need
> for any whitelist, so why not just the same logic for the kernel
> commandline? In fact, that should already work without this patch,
> should it not (didn't actually try, just looked at the code)?
>
> "root=none rootfstype=tmpfs"
>
> Cheers,
>
> Tom
>
> On Tue, Mar 24, 2015 at 12:52 AM, Tobias Hunger <tobias.hunger at gmail.com> wrote:
>> This allows for stateless systems.
>> ---
>>  src/fstab-generator/fstab-generator.c | 21 +++++++++++++--------
>>  src/shared/util.c                     | 30 ++++++++++++++++++++++++++++++
>>  src/shared/util.h                     |  1 +
>>  3 files changed, 44 insertions(+), 8 deletions(-)
>>
>> diff --git a/src/fstab-generator/fstab-generator.c b/src/fstab-generator/fstab-generator.c
>> index 2ece12f..77c97fd 100644
>> --- a/src/fstab-generator/fstab-generator.c
>> +++ b/src/fstab-generator/fstab-generator.c
>> @@ -397,15 +397,20 @@ static int add_root_mount(void) {
>>          _cleanup_free_ char *what = NULL;
>>          const char *opts;
>>
>> -        if (isempty(arg_root_what)) {
>> -                log_debug("Could not find a root= entry on the kernel command line.");
>> -                return 0;
>> -        }
>> +        if (fstype_is_deviceless(arg_root_fstype)) {
>> +                if (free_and_strdup(&what, arg_root_what) < 0)
>> +                        return log_oom();
>> +        } else {
>> +                if (isempty(arg_root_what)) {
>> +                        log_debug("Could not find a root= entry on the kernel command line.");
>> +                        return 0;
>> +                }
>>
>> -        what = fstab_node_to_udev_node(arg_root_what);
>> -        if (!path_is_absolute(what)) {
>> -                log_debug("Skipping entry what=%s where=/sysroot type=%s", what, strna(arg_root_fstype));
>> -                return 0;
>> +                what = fstab_node_to_udev_node(arg_root_what);
>> +                if (!path_is_absolute(what)) {
>> +                        log_debug("Skipping entry what=%s where=/sysroot type=%s", what, strna(arg_root_fstype));
>> +                        return 0;
>> +                }
>>          }
>>
>>          if (!arg_root_options)
>> diff --git a/src/shared/util.c b/src/shared/util.c
>> index ad548da..cb03527 100644
>> --- a/src/shared/util.c
>> +++ b/src/shared/util.c
>> @@ -1713,6 +1713,36 @@ bool fstype_is_network(const char *fstype) {
>>          return nulstr_contains(table, fstype);
>>  }
>>
>> +bool fstype_is_deviceless(const char *fstype) {
>> +        static const char table[] =
>> +                "autofs\0"
>> +                "bdev\0"
>> +                "cgroup\0"
>> +                "configfs\0"
>> +                "cpuset\0"
>> +                "debugfs\0"
>> +                "devpts\0"
>> +                "devtmpfs\0"
>> +                "efivarfs\0"
>> +                "hugetlbfs\0"
>> +                "mqueue\0"
>> +                "nfs\0"
>> +                "nfs4\0"
>> +                "overlayfs\0"
>> +                "pipefs\0"
>> +                "proc\0"
>> +                "pstore\0"
>> +                "ramfs\0"
>> +                "rootfs\0"
>> +                "rpc_pipefs\0"
>> +                "securityfs\0"
>> +                "sockfs\0"
>> +                "sysfs\0"
>> +                "tmpfs\0";
>> +
>> +        return nulstr_contains(table, fstype);
>> +}
>> +
>>  int chvt(int vt) {
>>          _cleanup_close_ int fd;
>>
>> diff --git a/src/shared/util.h b/src/shared/util.h
>> index 29e85bb..b5f44b8 100644
>> --- a/src/shared/util.h
>> +++ b/src/shared/util.h
>> @@ -409,6 +409,7 @@ int fd_cloexec(int fd, bool cloexec);
>>  int close_all_fds(const int except[], unsigned n_except);
>>
>>  bool fstype_is_network(const char *fstype);
>> +bool fstype_is_deviceless(const char *fstype);
>>
>>  int chvt(int vt);
>>
>> --
>> 2.3.3
>>
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