Messages in this thread Patch in this message | | | Date | Thu, 03 Apr 2014 20:13:50 +0200 | From | Thomas Bächler <> | Subject | Re: Initramfs FSID altered in 3.14 |
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Am 03.04.2014 19:57, schrieb Dave Reisner: > Hi, > > [This is a repost of a G+ post at Tejun's request] > > With Linux 3.14, you might notice in /proc/self/mountinfo that your > root's parent FSID is now 0, instead of the 1 that it's been for the > last N years. Tejun wrote the change (9e30cc9595303b27b48) that caused > this, but the change comes in a rather innocuous way. Instead of an > internal kernel mount of sysfs being assigned 0, it's now the initramfs. > > So far, this has already caused switch_root and findmnt (from > util-linux) to break, cp (from coreutils) to break when using the -x > flag in early userspace, and it's also been pointed out that systemd's > readahead code makes assumptions about a device number of 0. > > Are we now supposed to go and change all the assumptions in userspace > about 0 being special? I'm conflicted. The kernel isn't supposed to > break userspace, but it seems to me that FSIDs were never something to > rely on -- similar to the block device numbering scheme.
Most of these bugs were not caused by rootfs' FSID being different from 1, but rather because there was a file system with FSID 0.
Only util-linux/switch_root assumed that rootfs always had exactly FSID 1 - which is IMO a wrong assumption.
However, tt seems that people have been assuming that st_dev > 0 for a while. If we want to revert this in the kernel, this patch (untested) should be sufficient:
diff --git a/fs/super.c b/fs/super.c index 80d5cf2..d9fddde 100644 --- a/fs/super.c +++ b/fs/super.c @@ -802,7 +802,7 @@ void emergency_remount(void) static DEFINE_IDA(unnamed_dev_ida); static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */ -static int unnamed_dev_start = 0; /* don't bother trying below it */ +static int unnamed_dev_start = 1; /* don't bother trying below it */ int get_anon_bdev(dev_t *p) {
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