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Message-Id: <E1KXjLj-0001FB-2h@pomaz-ex.szeredi.hu>
Date: Mon, 25 Aug 2008 23:11:43 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: randy.dunlap@...cle.com
CC: hch@...radead.org, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, miklos@...redi.hu
Subject: Re: [PATCH v2] documentation: split and build smount.c
On Mon, 18 Aug 2008, Randy Dunlap wrote:
> On Mon, 18 Aug 2008 01:04:31 -0400 Christoph Hellwig wrote:
>
> > Just remove it, and modern /bin/mount handles shared subtrees just fine
>
> Miklos... ?
Yes, ACK from me too. Thanks Randy!
Miklos
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> From: Randy Dunlap <randy.dunlap@...cle.com>
>
> mount(8) handles shared subtrees just fine, so remove the smount
> program from Documentation/filesystems/sharedsubtree.txt.
>
> Fix annoying "Lets" -> "Let's".
>
> Signed-off-by: Randy Dunlap <randy.dunlap@...cle.com>
> cc: Miklos Szeredi <miklos@...redi.hu>
> ---
> Documentation/filesystems/sharedsubtree.txt | 192 +++-------------------------
> 1 file changed, 25 insertions(+), 167 deletions(-)
>
> --- lin2627-rc3g4-kerndoc.orig/Documentation/filesystems/sharedsubtree.txt
> +++ lin2627-rc3g4-kerndoc/Documentation/filesystems/sharedsubtree.txt
> @@ -41,12 +41,11 @@ replicas continue to be exactly same.
>
> Here is an example:
>
> - Lets say /mnt has a mount that is shared.
> + Let's say /mnt has a mount that is shared.
> mount --make-shared /mnt
>
> - note: mount command does not yet support the --make-shared flag.
> - I have included a small C program which does the same by executing
> - 'smount /mnt shared'
> + Note: mount(8) command now supports the --make-shared flag,
> + so the sample 'smount' program is no longer needed.
>
> #mount --bind /mnt /tmp
> The above command replicates the mount at /mnt to the mountpoint /tmp
> @@ -58,7 +57,7 @@ replicas continue to be exactly same.
> #ls /tmp
> a b c
>
> - Now lets say we mount a device at /tmp/a
> + Now let's say we mount a device at /tmp/a
> #mount /dev/sd0 /tmp/a
>
> #ls /tmp/a
> @@ -80,20 +79,19 @@ replicas continue to be exactly same.
>
> Here is an example:
>
> - Lets say /mnt has a mount which is shared.
> + Let's say /mnt has a mount which is shared.
> #mount --make-shared /mnt
>
> - Lets bind mount /mnt to /tmp
> + Let's bind mount /mnt to /tmp
> #mount --bind /mnt /tmp
>
> the new mount at /tmp becomes a shared mount and it is a replica of
> the mount at /mnt.
>
> - Now lets make the mount at /tmp; a slave of /mnt
> + Now let's make the mount at /tmp; a slave of /mnt
> #mount --make-slave /tmp
> - [or smount /tmp slave]
>
> - lets mount /dev/sd0 on /mnt/a
> + let's mount /dev/sd0 on /mnt/a
> #mount /dev/sd0 /mnt/a
>
> #ls /mnt/a
> @@ -104,7 +102,7 @@ replicas continue to be exactly same.
>
> Note the mount event has propagated to the mount at /tmp
>
> - However lets see what happens if we mount something on the mount at /tmp
> + However let's see what happens if we mount something on the mount at /tmp
>
> #mount /dev/sd1 /tmp/b
>
> @@ -124,12 +122,11 @@ replicas continue to be exactly same.
>
> 2d) A unbindable mount is a unbindable private mount
>
> - lets say we have a mount at /mnt and we make is unbindable
> + let's say we have a mount at /mnt and we make is unbindable
>
> #mount --make-unbindable /mnt
> - [ smount /mnt unbindable ]
>
> - Lets try to bind mount this mount somewhere else.
> + Let's try to bind mount this mount somewhere else.
> # mount --bind /mnt /tmp
> mount: wrong fs type, bad option, bad superblock on /mnt,
> or too many mounted file systems
> @@ -139,147 +136,8 @@ replicas continue to be exactly same.
>
> 3) smount command
>
> - Currently the mount command is not aware of shared subtree features.
> - Work is in progress to add the support in mount ( util-linux package ).
> - Till then use the following program.
> -
> - ------------------------------------------------------------------------
> - //
> - //this code was developed my Miklos Szeredi <miklos@...redi.hu>
> - //and modified by Ram Pai <linuxram@...ibm.com>
> - // sample usage:
> - // smount /tmp shared
> - //
> - #include <stdio.h>
> - #include <stdlib.h>
> - #include <unistd.h>
> - #include <string.h>
> - #include <sys/mount.h>
> - #include <sys/fsuid.h>
> -
> - #ifndef MS_REC
> - #define MS_REC 0x4000 /* 16384: Recursive loopback */
> - #endif
> -
> - #ifndef MS_SHARED
> - #define MS_SHARED 1<<20 /* Shared */
> - #endif
> -
> - #ifndef MS_PRIVATE
> - #define MS_PRIVATE 1<<18 /* Private */
> - #endif
> -
> - #ifndef MS_SLAVE
> - #define MS_SLAVE 1<<19 /* Slave */
> - #endif
> -
> - #ifndef MS_UNBINDABLE
> - #define MS_UNBINDABLE 1<<17 /* Unbindable */
> - #endif
> -
> - int main(int argc, char *argv[])
> - {
> - int type;
> - if(argc != 3) {
> - fprintf(stderr, "usage: %s dir "
> - "<rshared|rslave|rprivate|runbindable|shared|slave"
> - "|private|unbindable>\n" , argv[0]);
> - return 1;
> - }
> -
> - fprintf(stdout, "%s %s %s\n", argv[0], argv[1], argv[2]);
> -
> - if (strcmp(argv[2],"rshared")==0)
> - type=(MS_SHARED|MS_REC);
> - else if (strcmp(argv[2],"rslave")==0)
> - type=(MS_SLAVE|MS_REC);
> - else if (strcmp(argv[2],"rprivate")==0)
> - type=(MS_PRIVATE|MS_REC);
> - else if (strcmp(argv[2],"runbindable")==0)
> - type=(MS_UNBINDABLE|MS_REC);
> - else if (strcmp(argv[2],"shared")==0)
> - type=MS_SHARED;
> - else if (strcmp(argv[2],"slave")==0)
> - type=MS_SLAVE;
> - else if (strcmp(argv[2],"private")==0)
> - type=MS_PRIVATE;
> - else if (strcmp(argv[2],"unbindable")==0)
> - type=MS_UNBINDABLE;
> - else {
> - fprintf(stderr, "invalid operation: %s\n", argv[2]);
> - return 1;
> - }
> - setfsuid(getuid());
> -
> - if(mount("", argv[1], "dontcare", type, "") == -1) {
> - perror("mount");
> - return 1;
> - }
> - return 0;
> - }
> - -----------------------------------------------------------------------
> -
> - Copy the above code snippet into smount.c
> - gcc -o smount smount.c
> -
> -
> - (i) To mark all the mounts under /mnt as shared execute the following
> - command:
> -
> - smount /mnt rshared
> - the corresponding syntax planned for mount command is
> - mount --make-rshared /mnt
> -
> - just to mark a mount /mnt as shared, execute the following
> - command:
> - smount /mnt shared
> - the corresponding syntax planned for mount command is
> - mount --make-shared /mnt
> -
> - (ii) To mark all the shared mounts under /mnt as slave execute the
> - following
> -
> - command:
> - smount /mnt rslave
> - the corresponding syntax planned for mount command is
> - mount --make-rslave /mnt
> -
> - just to mark a mount /mnt as slave, execute the following
> - command:
> - smount /mnt slave
> - the corresponding syntax planned for mount command is
> - mount --make-slave /mnt
> -
> - (iii) To mark all the mounts under /mnt as private execute the
> - following command:
> -
> - smount /mnt rprivate
> - the corresponding syntax planned for mount command is
> - mount --make-rprivate /mnt
> -
> - just to mark a mount /mnt as private, execute the following
> - command:
> - smount /mnt private
> - the corresponding syntax planned for mount command is
> - mount --make-private /mnt
> -
> - NOTE: by default all the mounts are created as private. But if
> - you want to change some shared/slave/unbindable mount as
> - private at a later point in time, this command can help.
> -
> - (iv) To mark all the mounts under /mnt as unbindable execute the
> - following
> -
> - command:
> - smount /mnt runbindable
> - the corresponding syntax planned for mount command is
> - mount --make-runbindable /mnt
> -
> - just to mark a mount /mnt as unbindable, execute the following
> - command:
> - smount /mnt unbindable
> - the corresponding syntax planned for mount command is
> - mount --make-unbindable /mnt
> + Modern mount(8) command is aware of shared subtree features,
> + so use it instead of the 'smount' command. [source code removed]
>
>
> 4) Use cases
> @@ -558,7 +416,7 @@ replicas continue to be exactly same.
> then the subtree under the unbindable mount is pruned in the new
> location.
>
> - eg: lets say we have the following mount tree.
> + eg: let's say we have the following mount tree.
>
> A
> / \
> @@ -566,7 +424,7 @@ replicas continue to be exactly same.
> / \ / \
> D E F G
>
> - Lets say all the mount except the mount C in the tree are
> + Let's say all the mount except the mount C in the tree are
> of a type other than unbindable.
>
> If this tree is rbound to say Z
> @@ -683,13 +541,13 @@ replicas continue to be exactly same.
> 'b' on mounts that receive propagation from mount 'B' and does not have
> sub-mounts within them are unmounted.
>
> - Example: Lets say 'B1', 'B2', 'B3' are shared mounts that propagate to
> + Example: Let's say 'B1', 'B2', 'B3' are shared mounts that propagate to
> each other.
>
> - lets say 'A1', 'A2', 'A3' are first mounted at dentry 'b' on mount
> + let's say 'A1', 'A2', 'A3' are first mounted at dentry 'b' on mount
> 'B1', 'B2' and 'B3' respectively.
>
> - lets say 'C1', 'C2', 'C3' are next mounted at the same dentry 'b' on
> + let's say 'C1', 'C2', 'C3' are next mounted at the same dentry 'b' on
> mount 'B1', 'B2' and 'B3' respectively.
>
> if 'C1' is unmounted, all the mounts that are most-recently-mounted on
> @@ -710,7 +568,7 @@ replicas continue to be exactly same.
> A cloned namespace contains all the mounts as that of the parent
> namespace.
>
> - Lets say 'A' and 'B' are the corresponding mounts in the parent and the
> + Let's say 'A' and 'B' are the corresponding mounts in the parent and the
> child namespace.
>
> If 'A' is shared, then 'B' is also shared and 'A' and 'B' propagate to
> @@ -759,11 +617,11 @@ replicas continue to be exactly same.
> mount --make-slave /mnt
>
> At this point we have the first mount at /tmp and
> - its root dentry is 1. Lets call this mount 'A'
> + its root dentry is 1. Let's call this mount 'A'
> And then we have a second mount at /tmp1 with root
> - dentry 2. Lets call this mount 'B'
> + dentry 2. Let's call this mount 'B'
> Next we have a third mount at /mnt with root dentry
> - mnt. Lets call this mount 'C'
> + mnt. Let's call this mount 'C'
>
> 'B' is the slave of 'A' and 'C' is a slave of 'B'
> A -> B -> C
> @@ -794,7 +652,7 @@ replicas continue to be exactly same.
>
> Q3 Why is unbindable mount needed?
>
> - Lets say we want to replicate the mount tree at multiple
> + Let's say we want to replicate the mount tree at multiple
> locations within the same subtree.
>
> if one rbind mounts a tree within the same subtree 'n' times
> @@ -803,7 +661,7 @@ replicas continue to be exactly same.
> mounts. Here is a example.
>
> step 1:
> - lets say the root tree has just two directories with
> + let's say the root tree has just two directories with
> one vfsmount.
> root
> / \
> @@ -875,7 +733,7 @@ replicas continue to be exactly same.
> Unclonable mounts come in handy here.
>
> step 1:
> - lets say the root tree has just two directories with
> + let's say the root tree has just two directories with
> one vfsmount.
> root
> / \
>
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