Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756751AbYHSBQU (ORCPT ); Mon, 18 Aug 2008 21:16:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756633AbYHSBPj (ORCPT ); Mon, 18 Aug 2008 21:15:39 -0400 Received: from agminet01.oracle.com ([141.146.126.228]:37092 "EHLO agminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756540AbYHSBPh (ORCPT ); Mon, 18 Aug 2008 21:15:37 -0400 Date: Mon, 18 Aug 2008 18:14:09 -0700 From: Randy Dunlap To: Christoph Hellwig Cc: lkml , akpm , miklos@szeredi.hu Subject: [PATCH v2] documentation: split and build smount.c Message-Id: <20080818181409.f2861821.randy.dunlap@oracle.com> In-Reply-To: <20080818050431.GA20692@infradead.org> References: <20080817214442.ca4345ce.randy.dunlap@oracle.com> <20080818050431.GA20692@infradead.org> Organization: Oracle Linux Eng. X-Mailer: Sylpheed 2.5.0 (GTK+ 2.12.0; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: AAAAAQAAAAI= X-Brightmail-Tracker: AAAAAQAAAAI= X-Whitelist: TRUE X-Whitelist: TRUE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10670 Lines: 337 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... ? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ From: Randy Dunlap 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 cc: Miklos Szeredi --- 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 - //and modified by Ram Pai - // sample usage: - // smount /tmp shared - // - #include - #include - #include - #include - #include - #include - - #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 " - "\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 / \ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/