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authorJustus Winter <4winter@informatik.uni-hamburg.de>2013-11-14 15:36:36 +0100
committerJustus Winter <4winter@informatik.uni-hamburg.de>2014-01-12 15:58:59 +0100
commit8070f62fb5240ee5b924d0dae501a50f4662ffe9 (patch)
treea7fe95dddeda956e75da564e99e8d4baf801954c
parent19689c97a05e0a10691b671c4c37ca0bf51bdd2b (diff)
trans/mtab: populate mtab objects on demand
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.
-rw-r--r--trans/mtab.c49
1 files changed, 47 insertions, 2 deletions
diff --git a/trans/mtab.c b/trans/mtab.c
index 250de7d6..9b867b7b 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;
}