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Message-Id: <1198874586335-git-send-email-ezk@cs.sunysb.edu> Date: Fri, 28 Dec 2007 15:42:38 -0500 From: Erez Zadok <ezk@...sunysb.edu> To: akpm@...ux-foundation.org Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, viro@....linux.org.uk, hch@...radead.org, Erez Zadok <ezk@...sunysb.edu>, Michael Tokarev <mjt@....msk.ru> Subject: [PATCH 04/30] Unionfs: clarify usage.txt read/write behavior CC: Michael Tokarev <mjt@....msk.ru> Signed-off-by: Erez Zadok <ezk@...sunysb.edu> --- Documentation/filesystems/unionfs/concepts.txt | 20 +++++++++++++++++--- Documentation/filesystems/unionfs/issues.txt | 2 +- Documentation/filesystems/unionfs/usage.txt | 13 ++++++++----- 3 files changed, 26 insertions(+), 9 deletions(-) diff --git a/Documentation/filesystems/unionfs/concepts.txt b/Documentation/filesystems/unionfs/concepts.txt index 7654ccc..bed69bd 100644 --- a/Documentation/filesystems/unionfs/concepts.txt +++ b/Documentation/filesystems/unionfs/concepts.txt @@ -1,4 +1,4 @@ -Unionfs 2.1 CONCEPTS: +Unionfs 2.x CONCEPTS: ===================== This file describes the concepts needed by a namespace unification file @@ -66,12 +66,26 @@ Copyup: ======= When a change is made to the contents of a file's data or meta-data, they -have to be stored somewhere. The best way is to create a copy of the +have to be stored somewhere. The best way is to create a copy of the original file on a branch that is writable, and then redirect the write -though to this copy. The copy must be made on a higher priority branch so +though to this copy. The copy must be made on a higher priority branch so that lookup and readdir return this newer "version" of the file rather than the original (see duplicate elimination). +An entire unionfs mount can be read-only or read-write. If it's read-only, +then none of the branches will be written to, even if some of the branches +are physically writeable. If the unionfs mount is read-write, then the +leftmost (highest priority) branch must be writeable (for copyup to take +place); the remaining branches can be any mix of read-write and read-only. + +In a writeable mount, unionfs will create new files/dir in the leftmost +branch. If one tries to modify a file in a read-only branch/media, unionfs +will copyup the file to the leftmost branch and modify it there. If you try +to modify a file from a writeable branch which is not the leftmost branch, +then unionfs will modify it in that branch; this is useful if you, say, +unify differnet packages (e.g., apache, sendmail, ftpd, etc.) and you want +changes to specific package files to remain logically in the directory where +they came from. Cache Coherency: ================ diff --git a/Documentation/filesystems/unionfs/issues.txt b/Documentation/filesystems/unionfs/issues.txt index 9db1d70..bb6ab05 100644 --- a/Documentation/filesystems/unionfs/issues.txt +++ b/Documentation/filesystems/unionfs/issues.txt @@ -1,4 +1,4 @@ -KNOWN Unionfs 2.1 ISSUES: +KNOWN Unionfs 2.x ISSUES: ========================= 1. Unionfs should not use lookup_one_len() on the underlying f/s as it diff --git a/Documentation/filesystems/unionfs/usage.txt b/Documentation/filesystems/unionfs/usage.txt index 59c4f28..1adde69 100644 --- a/Documentation/filesystems/unionfs/usage.txt +++ b/Documentation/filesystems/unionfs/usage.txt @@ -12,7 +12,7 @@ GENERAL SYNTAX # mount -t unionfs -o <OPTIONS>,<BRANCH-OPTIONS> none MOUNTPOINT -OPTIONS can be any legal combination one of: +OPTIONS can be any legal combination of: - ro # mount file system read-only - rw # mount file system read-write @@ -20,8 +20,9 @@ OPTIONS can be any legal combination one of: - incgen # increment generation no. (see Cache Consistency below) BRANCH-OPTIONS can be either (1) a list of branches given to the "dirs=" -option, or (2) a list of individual branch manipulation commands, described -in the "Branch Management" section below. +option, or (2) a list of individual branch manipulation commands, combined +with the "remount" option, and is further described in the "Branch +Management" section below. The syntax for the "dirs=" mount option is: @@ -32,7 +33,9 @@ the union, with an optional branch mode for each of those directories. Directories that come earlier (specified first, on the left) in the list have a higher precedence than those which come later. Additionally, read-only or read-write permissions of the branch can be specified by -appending =ro or =rw (default) to each directory. +appending =ro or =rw (default) to each directory. See the Copyup section in +concepts.txt, for a description of Unionfs's behavior when mixing read-only +and read-write branches and mounts. Syntax: @@ -112,7 +115,7 @@ CACHE CONSISTENCY ================= If you modify any file on any of the lower branches directly, while there is -a Unionfs 2.1 mounted above any of those branches, you should tell Unionfs +a Unionfs 2.x mounted above any of those branches, you should tell Unionfs to purge its caches and re-get the objects. To do that, you have to increment the generation number of the superblock using the following command: -- 1.5.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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