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[PATCH 1/8] trans/mtab: populate mtab objects on demand
From: |
Justus Winter |
Subject: |
[PATCH 1/8] trans/mtab: populate mtab objects on demand |
Date: |
Sun, 12 Jan 2014 20:08:38 +0100 |
Previously the mtab content was generated in the open hook. Delay this
until the data is needed. A follow up patch will take advantage of
this to both simplify the logic in mtab_populate and make it more
robust at the same time.
* trans/mtab.c (open_hook): Do not eagerly populate the mtab.
(trivfs_S_io_read): Populate the mtab struct on demand.
(trivfs_S_io_seek): Likewise.
(trivfs_S_io_readable): Likewise.
---
trans/mtab.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 47 insertions(+), 2 deletions(-)
diff --git a/trans/mtab.c b/trans/mtab.c
index 250de7d..9b867b7 100644
--- a/trans/mtab.c
+++ b/trans/mtab.c
@@ -1,6 +1,6 @@
/* This is an mtab translator.
- Copyright (C) 2013 Free Software Foundation, Inc.
+ Copyright (C) 2013,14 Free Software Foundation, Inc.
Written by Justus Winter <4winter@informatik.uni-hamburg.de>
@@ -594,7 +594,30 @@ open_hook (struct trivfs_peropen *peropen)
mtab->contents = NULL;
mtab->contents_len = 0;
- return mtab_populate (mtab, target_path, insecure);
+ /* The mtab object is initialized, but not yet populated. We delay
+ that until that data is really needed. This avoids the following
+ problems:
+
+ Suppose you have
+
+ settrans -ac /foo /hurd/mtab /
+
+ If you now access /foo, the mtab translator will walk the tree of
+ all active translators starting from /. If it visits /foo, it
+ will talk to itself. Previously the translator migitated this by
+ comparing the control port of the translator with its own. This
+ does not work if you got two mtab translators like this:
+
+ settrans -ac /foo /hurd/mtab /
+ settrans -ac /bar /hurd/mtab /
+
+ With a single-threaded mtab server this results in a dead-lock,
+ with a multi-threaded server this will create more and more
+ threads.
+
+ Delaying the data generation until it is really needed cleanly
+ avoids these kind of problems. */
+ return 0;
}
static void
@@ -624,6 +647,14 @@ trivfs_S_io_read (struct trivfs_protid *cred,
/* Get the offset. */
op = cred->po->hook;
+
+ if (op->contents == NULL)
+ {
+ error_t err = mtab_populate (op, target_path, insecure);
+ if (err)
+ return err;
+ }
+
if (offs == -1)
offs = op->offs;
@@ -666,6 +697,13 @@ trivfs_S_io_seek (struct trivfs_protid *cred,
struct mtab *op = cred->po->hook;
+ if (op->contents == NULL)
+ {
+ error_t err = mtab_populate (op, target_path, insecure);
+ if (err)
+ return err;
+ }
+
switch (whence)
{
case SEEK_CUR:
@@ -711,6 +749,13 @@ trivfs_S_io_readable (struct trivfs_protid *cred,
struct mtab *op = cred->po->hook;
+ if (op->contents == NULL)
+ {
+ error_t err = mtab_populate (op, target_path, insecure);
+ if (err)
+ return err;
+ }
+
*amount = op->contents_len - op->offs;
return 0;
}
--
1.8.5.2
- [PATCH 1/8] trans/mtab: populate mtab objects on demand,
Justus Winter <=
- [PATCH 2/8] trans/mtab: remove the loop detection logic, Justus Winter, 2014/01/12
- [PATCH 4/8] trans/mtab: make the translator multithreaded, Justus Winter, 2014/01/12
- [PATCH 3/8] trans/mtab: properly lock mtab objects, Justus Winter, 2014/01/12
- [PATCH 5/8] trans/mtab: do not include non-filesystem translators by default, Justus Winter, 2014/01/12
- [PATCH 6/8] libfshelp: fix the api of fshelp_set_active_translator, Justus Winter, 2014/01/12