rootfs: force mounting rootfs as tmpfs

Commit 16203a7a9422 ("initmpfs: make rootfs use tmpfs when CONFIG_TMPFS enabled") introduced using tmpfs as the rootfs filesystem. The use of tmpfs is limited to systems that do not specify "root=" on the boot command line.

Without the check "!saved_root_name[0]", rootfs uses tmpfs. As there must be a valid reason for this check, this patch introduces a new boot command line option named "noramfs" to force rootfs to use tmpfs.

Signed-off-by Mimi Zohar <[email protected]>

---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 init/do_mounts.c                                | 15 +++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

Quoted 10 lines · Mimi Zohar

Commit 16203a7a9422 ("initmpfs: make rootfs use tmpfs when CONFIG_TMPFS enabled") introduced using tmpfs as the rootfs filesystem. The use of tmpfs is limited to systems that do not specify "root=" on the boot command line.

Without the check "!saved_root_name[0]", rootfs uses tmpfs. As there must be a valid reason for this check, this patch introduces a new boot command line option named "noramfs" to force rootfs to use tmpfs.

Signed-off-by Mimi Zohar <[email protected]>

How about just:

init/do_mounts.c +2 -2

index 7cf4f6d..af66ede 100644
@@ -632,8 +632,8 @@ int __init init_rootfs(void)
 	if (err)
 		return err;
 
-	if (IS_ENABLED(CONFIG_TMPFS) && !saved_root_name[0] &&
-		(!root_fs_names || strstr(root_fs_names, "tmpfs"))) {
+	if (IS_ENABLED(CONFIG_TMPFS) && (!saved_root_name[0] ||
+		!strcmp(saved_root_name, "tmpfs"))) {
 		err = shmem_init();
 		is_tmpfs = true;
 	} else {

(Obviously-signed-off-by: Rob Landley <rob-VoJi6FS/[email protected]>)

I.E. if you somehow just can't stop yourself from specifying root= when using rootfs, have "root=tmpfs" do what you want.

(The old "I configured in tmpfs and am using rootfs but I want that rootfs to be ramfs, not tmpfs" code doesn't seem to be a real-world concern, does it?)

Quoted 5 lines

---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 init/do_mounts.c                                | 15 +++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

I suppose I should do a documentation update too. Lemme send a proper one after work...

Rob

P.S. While I'm at it, I've meant to wire up rootflags= so you can specify a memory limit other than 50% forever, I should do that too. And resend my "make DEVTMPFS_MOUNT apply to initramfs" patch (with the debian bug workaround)...

On Wed, 2018-01-31 at 13:32 -0600, Rob Landley wrote:>> (The old "I configured in tmpfs and am using rootfs but I want that

Quoted 2 lines

to be ramfs, not tmpfs" code doesn't seem to be a real-world concern, does it?)

I must be missing something.  Which systems don't specify "root=" on the boot command line.

If we want to include and restore xattrs,
there needs to be a way of using tmpfs.

Mimi

Quoted 1 line · Mimi Zohar

On Wed, 2018-01-31 at 13:32 -0600, Rob Landley wrote:>> (The old "I configured in tmpfs and am using rootfs but I want that

rootfs

Quoted 5 lines

Quoted 2 lines

to be ramfs, not tmpfs" code doesn't seem to be a real-world concern, does it?)

I must be missing something.  Which systems don't specify "root=" on the boot command line.

Any system using initrd or initramfs?

Quoted 6 lines · Rob Landley

Quoted 1 line · Mimi Zohar

On Wed, 2018-01-31 at 13:32 -0600, Rob Landley wrote:>> (The old "I configured in tmpfs and am using rootfs but I want that

rootfs

Quoted 3 lines

Quoted 2 lines

to be ramfs, not tmpfs" code doesn't seem to be a real-world concern, does it?)

Quoted 5 lines

Quoted 2 lines

I must be missing something.  Which systems don't specify "root=" on the boot command line.

Any system using initrd or initramfs?

Don't a lot of initramfs setups use root= to tell the initramfs which actual root file system to switch to after early boot?

Quoted 7 lines · Arvind Sankar

Quoted 6 lines · Rob Landley

Quoted 1 line · Mimi Zohar

On Wed, 2018-01-31 at 13:32 -0600, Rob Landley wrote:>> (The old "I configured in tmpfs and am using rootfs but I want that

rootfs

Quoted 3 lines

Quoted 2 lines

to be ramfs, not tmpfs" code doesn't seem to be a real-world concern, does it?)

Quoted 8 lines

Quoted 5 lines

Quoted 2 lines

I must be missing something.  Which systems don't specify "root=" on the boot command line.

Any system using initrd or initramfs?

Don't a lot of initramfs setups use root= to tell the initramfs which actual root file system to switch to after early boot?

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

Quoted 4 lines

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

[googles]... I do not understand why this package exists.

If you're switching to another root filesystem, using a tool that wikipedia[citation needed] says has no purpose but to switch to another root filesystem, (so let's reproduce the kernel infrastructure in userspace while leaving it the kernel too)... why do you need initramfs to be tmpfs? You're using it for half a second, then discarding it, what's the point of it being tmpfs?

Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs is configured in, even when you're then going to overmount it with something else like you're doing, let's just _remove_ the test. If it can be tmpfs, have it be tmpfs.

Quoted 5 lines · Rob Landley

Quoted 4 lines

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

Quoted 8 lines

[googles]... I do not understand why this package exists.

If you're switching to another root filesystem, using a tool that wikipedia[citation needed] says has no purpose but to switch to another root filesystem, (so let's reproduce the kernel infrastructure in userspace while leaving it the kernel too)... why do you need initramfs to be tmpfs? You're using it for half a second, then discarding it, what's the point of it being tmpfs?

Unlike the kernel image which is signed by the distros, the initramfs doesn't come signed, because it is built on the target system.  Even if the initramfs did come signed, it is beneficial to measure and appraise the individual files in the initramfs.

Quoted 4 lines

Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs is configured in, even when you're then going to overmount it with something else like you're doing, let's just _remove_ the test. If it can be tmpfs, have it be tmpfs.

Very much appreciated!

Quoted 16 lines · Mimi Zohar

Quoted 5 lines · Rob Landley

Quoted 4 lines

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

Quoted 8 lines

[googles]... I do not understand why this package exists.

If you're switching to another root filesystem, using a tool that wikipedia[citation needed] says has no purpose but to switch to another root filesystem, (so let's reproduce the kernel infrastructure in userspace while leaving it the kernel too)... why do you need initramfs to be tmpfs? You're using it for half a second, then discarding it, what's the point of it being tmpfs?

Quoted 4 lines

Unlike the kernel image which is signed by the distros, the initramfs doesn't come signed, because it is built on the target system.  Even if the initramfs did come signed, it is beneficial to measure and appraise the individual files in the initramfs.

You can still shoot yourself in the foot with tmpfs. People mount a /run and a /tmp and then as a normal user you can go
https://twitter.com/landley/status/959103235305951233 and maybe the default should be a little more clever there...

I'll throw it on the todo heap. :)

Quoted 5 lines

Quoted 4 lines

Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs is configured in, even when you're then going to overmount it with something else like you're doing, let's just _remove_ the test. If it can be tmpfs, have it be tmpfs.

Quoted 1 line

Very much appreciated!

Not yet tested, but something like the attached? (Sorry for the half-finished doc changes in there, I'm at work and have a 5 minute break. I can test properly this evening if you don't get to it...)

Quoted 34 lines · Mimi Zohar

Quoted 16 lines · Rob Landley

Quoted 6 lines

Quoted 5 lines

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

Quoted 8 lines

[googles]... I do not understand why this package exists.

If you're switching to another root filesystem, using a tool that wikipedia[citation needed] says has no purpose but to switch to another root filesystem, (so let's reproduce the kernel infrastructure in userspace while leaving it the kernel too)... why do you need initramfs to be tmpfs? You're using it for half a second, then discarding it, what's the point of it being tmpfs?

Quoted 4 lines

Unlike the kernel image which is signed by the distros, the initramfs doesn't come signed, because it is built on the target system.  Even if the initramfs did come signed, it is beneficial to measure and appraise the individual files in the initramfs.

You can still shoot yourself in the foot with tmpfs. People mount a /run and a /tmp and then as a normal user you can go
https://twitter.com/landley/status/959103235305951233 and maybe the default should be a little more clever there...

I'll throw it on the todo heap. :)

Quoted 5 lines

Quoted 4 lines

Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs is configured in, even when you're then going to overmount it with something else like you're doing, let's just _remove_ the test. If it can be tmpfs, have it be tmpfs.

Quoted 5 lines

Quoted 1 line

Very much appreciated!

Not yet tested, but something like the attached? (Sorry for the half-finished doc changes in there, I'm at work and have a 5 minute break. I can test properly this evening if you don't get to it...)

Yes, rootfs is being mounted as tmpfs.

Quoting Mimi Zohar (2018-02-01 13:51:52)

Quoted 41 lines · Rob Landley

Quoted 39 lines · Mimi Zohar

Quoted 16 lines · Rob Landley

Quoted 6 lines

Quoted 5 lines

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

Quoted 8 lines

[googles]... I do not understand why this package exists.

If you're switching to another root filesystem, using a tool that wikipedia[citation needed] says has no purpose but to switch to another root filesystem, (so let's reproduce the kernel infrastructure in userspace while leaving it the kernel too)... why do you need initramfs to be tmpfs? You're using it for half a second, then discarding it, what's the point of it being tmpfs?

Quoted 4 lines

Unlike the kernel image which is signed by the distros, the initramfs doesn't come signed, because it is built on the target system.  Even if the initramfs did come signed, it is beneficial to measure and appraise the individual files in the initramfs.

You can still shoot yourself in the foot with tmpfs. People mount a /run and a /tmp and then as a normal user you can go
https://twitter.com/landley/status/959103235305951233 and maybe the default should be a little more clever there...

I'll throw it on the todo heap. :)

Quoted 6 lines

Quoted 4 lines

Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs is configured in, even when you're then going to overmount it with something else like you're doing, let's just _remove_ the test. If it can be tmpfs, have it be tmpfs.

Very much appreciated!

Not yet tested, but something like the attached? (Sorry for the half-finished doc changes in there, I'm at work and have a 5 minute break. I can test properly this evening if you don't get to it...)

Quoted 1 line

Yes, rootfs is being mounted as tmpfs.

I don't think you can unconditionally replace ramfs with initramfs by default. Their behavior is different in some cases (e.g. pivot_root vs switch_root)

and it can break many systems that expect ramfs by default.

Quoted 42 lines · Taras Kondratiuk

Quoting Mimi Zohar (2018-02-01 13:51:52)

Quoted 41 lines · Rob Landley

Quoted 39 lines · Mimi Zohar

Quoted 16 lines · Rob Landley

Quoted 6 lines

Quoted 5 lines

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue

Quoted 8 lines

[googles]... I do not understand why this package exists.

If you're switching to another root filesystem, using a tool that wikipedia[citation needed] says has no purpose but to switch to another root filesystem, (so let's reproduce the kernel infrastructure in userspace while leaving it the kernel too)... why do you need initramfs to be tmpfs? You're using it for half a second, then discarding it, what's the point of it being tmpfs?

Quoted 4 lines

Unlike the kernel image which is signed by the distros, the initramfs doesn't come signed, because it is built on the target system.  Even if the initramfs did come signed, it is beneficial to measure and appraise the individual files in the initramfs.

You can still shoot yourself in the foot with tmpfs. People mount a /run and a /tmp and then as a normal user you can go
https://twitter.com/landley/status/959103235305951233 and maybe the default should be a little more clever there...

I'll throw it on the todo heap. :)

Quoted 6 lines

Quoted 4 lines

Sigh. If people are ok with having rootfs just be tmpfs whenever tmpfs is configured in, even when you're then going to overmount it with something else like you're doing, let's just _remove_ the test. If it can be tmpfs, have it be tmpfs.

Very much appreciated!

Not yet tested, but something like the attached? (Sorry for the half-finished doc changes in there, I'm at work and have a 5 minute break. I can test properly this evening if you don't get to it...)

Quoted 5 lines

Quoted 1 line

Yes, rootfs is being mounted as tmpfs.

I don't think you can unconditionally replace ramfs with initramfs by default. Their behavior is different in some cases (e.g. pivot_root vs switch_root)

Both are switch_root, you can't pivot_root off of either one. (Yes, I hit that bug and reported it, and they fixed it, back in the day...
http://lists.busybox.net/pipermail/busybox/2006-March/053529.html )

Quoted 1 line

and it can break many systems that expect ramfs by default.

The use case I told Mimi about off-list (since they stopped cc:ing the list in one of their replies but the conversation continued) was the guy who was extracting an initramfs bigger than 50% of system memory, which worked with initramfs but failed with initmpfs. A quick google didn't find the original message but it resulted in this blog entry from the affected party:

http://www.lightofdawn.org/blog/?viewDetailed=00128

I.E. yeah, I know, I need to redo these patches tonight.

Quoted 13 lines · Arvind Sankar

Quoted 11 lines · Rob Landley

Quoted 1 line · Mimi Zohar

On Wed, 2018-01-31 at 13:32 -0600, Rob Landley wrote:>> (The old "I configured in tmpfs and am using rootfs but I want that

rootfs

Quoted 5 lines

Quoted 2 lines

to be ramfs, not tmpfs" code doesn't seem to be a real-world concern, does it?)

I must be missing something.  Which systems don't specify "root=" on the boot command line.

Any system using initrd or initramfs?

Quoted 2 lines

Don't a lot of initramfs setups use root= to tell the initramfs which actual root file system to switch to after early boot?

With your patch and specifying "root=tmpfs", dracut is complaining:

dracut: FATAL: Don't know how to handle 'root=tmpfs'
dracut: refusing to continue