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author | KaiGai Kohei <kaigai@ak.jp.nec.com> | 2006-05-13 15:14:14 +0900 |
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committer | KaiGai Kohei <kaigai@ak.jp.nec.com> | 2006-05-13 15:14:14 +0900 |
commit | 8b0b339d46ca0105a9936e3caa3bac80b72de7a3 (patch) | |
tree | 3849c24ba41edad67a610f4e584e41f803df23c5 /fs/jffs2/README.Locking | |
parent | de1f72fab35d2b6215017690c6dc27b8f4aa14bc (diff) | |
download | kernel_samsung_smdk4412-8b0b339d46ca0105a9936e3caa3bac80b72de7a3.zip kernel_samsung_smdk4412-8b0b339d46ca0105a9936e3caa3bac80b72de7a3.tar.gz kernel_samsung_smdk4412-8b0b339d46ca0105a9936e3caa3bac80b72de7a3.tar.bz2 |
[JFFS2][XATTR] Add a description about c->xattr_sem
Add a description about the c->xattr_sem read/write semaphore
into README.Locking.
[3/10] jffs2-xattr-v5.1-03-append_README.Locking.patch
Signed-off-by: KaiGai Kohei <kaigai@ak.jp.nec.com>
Diffstat (limited to 'fs/jffs2/README.Locking')
-rw-r--r-- | fs/jffs2/README.Locking | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/fs/jffs2/README.Locking b/fs/jffs2/README.Locking index b794343..c8f0bd6 100644 --- a/fs/jffs2/README.Locking +++ b/fs/jffs2/README.Locking @@ -150,3 +150,24 @@ the buffer. Ordering constraints: Lock wbuf_sem last, after the alloc_sem or and f->sem. + + + c->xattr_sem + ------------ + +This read/write semaphore protects against concurrent access to the +xattr related objects which include stuff in superblock and ic->xref. +In read-only path, write-semaphore is too much exclusion. It's enough +by read-semaphore. But you must hold write-semaphore when updating, +creating or deleting any xattr related object. + +Once xattr_sem released, there would be no assurance for the existence +of those objects. Thus, a series of processes is often required to retry, +when updating such a object is necessary under holding read semaphore. +For example, do_jffs2_getxattr() holds read-semaphore to scan xref and +xdatum at first. But it retries this process with holding write-semaphore +after release read-semaphore, if it's necessary to load name/value pair +from medium. + +Ordering constraints: + Lock xattr_sem last, after the alloc_sem. |