diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/devpts.txt | 145 | ||||
| -rw-r--r-- | Documentation/filesystems/ocfs2-online-filecheck.txt | 10 | ||||
| -rw-r--r-- | Documentation/filesystems/proc.txt | 2 |
3 files changed, 21 insertions, 136 deletions
diff --git a/Documentation/filesystems/devpts.txt b/Documentation/filesystems/devpts.txt index 30d2fcb32f72..9f94fe276dea 100644 --- a/Documentation/filesystems/devpts.txt +++ b/Documentation/filesystems/devpts.txt @@ -1,141 +1,26 @@ +Each mount of the devpts filesystem is now distinct such that ptys +and their indicies allocated in one mount are independent from ptys +and their indicies in all other mounts. -To support containers, we now allow multiple instances of devpts filesystem, -such that indices of ptys allocated in one instance are independent of indices -allocated in other instances of devpts. +All mounts of the devpts filesystem now create a /dev/pts/ptmx node +with permissions 0000. -To preserve backward compatibility, this support for multiple instances is -enabled only if: +To retain backwards compatibility the a ptmx device node (aka any node +created with "mknod name c 5 2") when opened will look for an instance +of devpts under the name "pts" in the same directory as the ptmx device +node. - - CONFIG_DEVPTS_MULTIPLE_INSTANCES=y, and - - '-o newinstance' mount option is specified while mounting devpts - -IOW, devpts now supports both single-instance and multi-instance semantics. - -If CONFIG_DEVPTS_MULTIPLE_INSTANCES=n, there is no change in behavior and -this referred to as the "legacy" mode. In this mode, the new mount options -(-o newinstance and -o ptmxmode) will be ignored with a 'bogus option' message -on console. - -If CONFIG_DEVPTS_MULTIPLE_INSTANCES=y and devpts is mounted without the -'newinstance' option (as in current start-up scripts) the new mount binds -to the initial kernel mount of devpts. This mode is referred to as the -'single-instance' mode and the current, single-instance semantics are -preserved, i.e PTYs are common across the system. - -The only difference between this single-instance mode and the legacy mode -is the presence of new, '/dev/pts/ptmx' node with permissions 0000, which -can safely be ignored. - -If CONFIG_DEVPTS_MULTIPLE_INSTANCES=y and 'newinstance' option is specified, -the mount is considered to be in the multi-instance mode and a new instance -of the devpts fs is created. Any ptys created in this instance are independent -of ptys in other instances of devpts. Like in the single-instance mode, the -/dev/pts/ptmx node is present. To effectively use the multi-instance mode, -open of /dev/ptmx must be a redirected to '/dev/pts/ptmx' using a symlink or -bind-mount. - -Eg: A container startup script could do the following: - - $ chmod 0666 /dev/pts/ptmx - $ rm /dev/ptmx - $ ln -s pts/ptmx /dev/ptmx - $ ns_exec -cm /bin/bash - - # We are now in new container - - $ umount /dev/pts - $ mount -t devpts -o newinstance lxcpts /dev/pts - $ sshd -p 1234 - -where 'ns_exec -cm /bin/bash' calls clone() with CLONE_NEWNS flag and execs -/bin/bash in the child process. A pty created by the sshd is not visible in -the original mount of /dev/pts. +As an option instead of placing a /dev/ptmx device node at /dev/ptmx +it is possible to place a symlink to /dev/pts/ptmx at /dev/ptmx or +to bind mount /dev/ptx/ptmx to /dev/ptmx. If you opt for using +the devpts filesystem in this manner devpts should be mounted with +the ptmxmode=0666, or chmod 0666 /dev/pts/ptmx should be called. Total count of pty pairs in all instances is limited by sysctls: kernel.pty.max = 4096 - global limit -kernel.pty.reserve = 1024 - reserve for initial instance +kernel.pty.reserve = 1024 - reserved for filesystems mounted from the initial mount namespace kernel.pty.nr - current count of ptys Per-instance limit could be set by adding mount option "max=<count>". This feature was added in kernel 3.4 together with sysctl kernel.pty.reserve. In kernels older than 3.4 sysctl kernel.pty.max works as per-instance limit. - -User-space changes ------------------- - -In multi-instance mode (i.e '-o newinstance' mount option is specified at least -once), following user-space issues should be noted. - -1. If -o newinstance mount option is never used, /dev/pts/ptmx can be ignored - and no change is needed to system-startup scripts. - -2. To effectively use multi-instance mode (i.e -o newinstance is specified) - administrators or startup scripts should "redirect" open of /dev/ptmx to - /dev/pts/ptmx using either a bind mount or symlink. - - $ mount -t devpts -o newinstance devpts /dev/pts - - followed by either - - $ rm /dev/ptmx - $ ln -s pts/ptmx /dev/ptmx - $ chmod 666 /dev/pts/ptmx - or - $ mount -o bind /dev/pts/ptmx /dev/ptmx - -3. The '/dev/ptmx -> pts/ptmx' symlink is the preferred method since it - enables better error-reporting and treats both single-instance and - multi-instance mounts similarly. - - But this method requires that system-startup scripts set the mode of - /dev/pts/ptmx correctly (default mode is 0000). The scripts can set the - mode by, either - - - adding ptmxmode mount option to devpts entry in /etc/fstab, or - - using 'chmod 0666 /dev/pts/ptmx' - -4. If multi-instance mode mount is needed for containers, but the system - startup scripts have not yet been updated, container-startup scripts - should bind mount /dev/ptmx to /dev/pts/ptmx to avoid breaking single- - instance mounts. - - Or, in general, container-startup scripts should use: - - mount -t devpts -o newinstance -o ptmxmode=0666 devpts /dev/pts - if [ ! -L /dev/ptmx ]; then - mount -o bind /dev/pts/ptmx /dev/ptmx - fi - - When all devpts mounts are multi-instance, /dev/ptmx can permanently be - a symlink to pts/ptmx and the bind mount can be ignored. - -5. A multi-instance mount that is not accompanied by the /dev/ptmx to - /dev/pts/ptmx redirection would result in an unusable/unreachable pty. - - mount -t devpts -o newinstance lxcpts /dev/pts - - immediately followed by: - - open("/dev/ptmx") - - would create a pty, say /dev/pts/7, in the initial kernel mount. - But /dev/pts/7 would be invisible in the new mount. - -6. The permissions for /dev/pts/ptmx node should be specified when mounting - /dev/pts, using the '-o ptmxmode=%o' mount option (default is 0000). - - mount -t devpts -o newinstance -o ptmxmode=0644 devpts /dev/pts - - The permissions can be later be changed as usual with 'chmod'. - - chmod 666 /dev/pts/ptmx - -7. A mount of devpts without the 'newinstance' option results in binding to - initial kernel mount. This behavior while preserving legacy semantics, - does not provide strict isolation in a container environment. i.e by - mounting devpts without the 'newinstance' option, a container could - get visibility into the 'host' or root container's devpts. - - To workaround this and have strict isolation, all mounts of devpts, - including the mount in the root container, should use the newinstance - option. diff --git a/Documentation/filesystems/ocfs2-online-filecheck.txt b/Documentation/filesystems/ocfs2-online-filecheck.txt index 1ab07860430d..139fab175c8a 100644 --- a/Documentation/filesystems/ocfs2-online-filecheck.txt +++ b/Documentation/filesystems/ocfs2-online-filecheck.txt @@ -5,12 +5,12 @@ This document will describe OCFS2 online file check feature. Introduction ============ -OCFS2 is often used in high-availaibility systems. However, OCFS2 usually +OCFS2 is often used in high-availability systems. However, OCFS2 usually converts the filesystem to read-only when encounters an error. This may not be necessary, since turning the filesystem read-only would affect other running processes as well, decreasing availability. Then, a mount option (errors=continue) is introduced, which would return the --EIO errno to the calling process and terminate furhter processing so that the +-EIO errno to the calling process and terminate further processing so that the filesystem is not corrupted further. The filesystem is not converted to read-only, and the problematic file's inode number is reported in the kernel log. The user can try to check/fix this file via online filecheck feature. @@ -44,7 +44,7 @@ There is a sysfs directory for each OCFS2 file system mounting: /sys/fs/ocfs2/<devname>/filecheck -Here, <devname> indicates the name of OCFS2 volumn device which has been already +Here, <devname> indicates the name of OCFS2 volume device which has been already mounted. The file above would accept inode numbers. This could be used to communicate with kernel space, tell which file(inode number) will be checked or fixed. Currently, three operations are supported, which includes checking @@ -76,14 +76,14 @@ The output is like this: This time, the <ERROR> column indicates whether this fix is successful or not. 3. The record cache is used to store the history of check/fix results. It's -defalut size is 10, and can be adjust between the range of 10 ~ 100. You can +default size is 10, and can be adjust between the range of 10 ~ 100. You can adjust the size like this: # echo "<size>" > /sys/fs/ocfs2/<devname>/filecheck/set Fixing stuff ============ -On receivng the inode, the filesystem would read the inode and the +On receiving the inode, the filesystem would read the inode and the file metadata. In case of errors, the filesystem would fix the errors and report the problems it fixed in the kernel log. As a precautionary measure, the inode must first be checked for errors before performing a final fix. diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index e8d00759bfa5..5b61eeae3f6e 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -725,7 +725,7 @@ IRQ, you can set it by doing: > echo 1 > /proc/irq/10/smp_affinity This means that only the first CPU will handle the IRQ, but you can also echo -5 which means that only the first and fourth CPU can handle the IRQ. +5 which means that only the first and third CPU can handle the IRQ. The contents of each smp_affinity file is the same by default: |