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authorUlrich Drepper <drepper@redhat.com>2003-05-17 20:53:32 +0000
committerUlrich Drepper <drepper@redhat.com>2003-05-17 20:53:32 +0000
commitfddfebbd1064dec313891ad91dd9ca6e92e622ec (patch)
treeed231a996e804653468ac2916a0d4b32628c0093 /nptl/sem_open.c
parent68a396e83a8e1e50d0dfde8ffb090a8df311453f (diff)
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Update.
2003-05-17 Ulrich Drepper <drepper@redhat.com> * sem_open.c: Fix one endless loop. Implement correct semantics wrt opening the same semaphore more then once. * sem_close.c: Adjust for sem_open change. * semaphoreP.h: Include <semaphore.h>. Define struct inuse_sem. Declare __sem_mappings, __sem_mappings_lock, __sem_search. * Makefile (tests): Add tst-sem7. * tst-sem7.c: New file.
Diffstat (limited to 'nptl/sem_open.c')
-rw-r--r--nptl/sem_open.c175
1 files changed, 156 insertions, 19 deletions
diff --git a/nptl/sem_open.c b/nptl/sem_open.c
index 2bfea63..374c7d8 100644
--- a/nptl/sem_open.c
+++ b/nptl/sem_open.c
@@ -22,6 +22,7 @@
#include <mntent.h>
#include <paths.h>
#include <pthread.h>
+#include <search.h>
#include <semaphore.h>
#include <stdarg.h>
#include <stdio.h>
@@ -122,11 +123,105 @@ __where_is_shmfs (void)
}
+/* Comparison function for search of existing mapping. */
+int
+attribute_hidden
+__sem_search (const void *a, const void *b)
+{
+ const struct inuse_sem *as = (const struct inuse_sem *) a;
+ const struct inuse_sem *bs = (const struct inuse_sem *) b;
+
+ if (as->ino != bs->ino)
+ /* Cannot return the difference the type is larger than int. */
+ return as->ino < bs->ino ? -1 : (as->ino == bs->ino ? 0 : 1);
+
+ if (as->dev != bs->dev)
+ /* Cannot return the difference the type is larger than int. */
+ return as->dev < bs->dev ? -1 : (as->dev == bs->dev ? 0 : 1);
+
+ return strcmp (as->name, bs->name);
+}
+
+
+/* The search tree for existing mappings. */
+void *__sem_mappings attribute_hidden;
+
+/* Lock to protect the search tree. */
+lll_lock_t __sem_mappings_lock = LLL_LOCK_INITIALIZER;
+
+
+/* Search for existing mapping and if possible add the one provided. */
+static sem_t *
+check_add_mapping (const char *name, size_t namelen, int fd, sem_t *existing)
+{
+ sem_t *result = SEM_FAILED;
+
+ /* Get the information about the file. */
+ struct stat64 st;
+ if (__fxstat64 (_STAT_VER, fd, &st) == 0)
+ {
+ /* Get the lock. */
+ lll_lock (__sem_mappings_lock);
+
+ /* Search for an existing mapping given the information we have. */
+ struct inuse_sem *fake;
+ fake = (struct inuse_sem *) alloca (sizeof (*fake) + namelen);
+ memcpy (fake->name, name, namelen);
+ fake->dev = st.st_dev;
+ fake->ino = st.st_ino;
+
+ struct inuse_sem **foundp = tfind (fake, &__sem_mappings, __sem_search);
+ if (foundp != NULL)
+ {
+ /* There is already a mapping. Use it. */
+ result = (*foundp)->sem;
+ ++(*foundp)->refcnt;
+ }
+ else if (existing != SEM_FAILED)
+ {
+ /* We haven't found a mapping but the caller has a mapping.
+ Install it. */
+ struct inuse_sem *newp;
+
+ newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen);
+ if (newp != NULL)
+ {
+ newp->dev = st.st_dev;
+ newp->ino = st.st_ino;
+ newp->refcnt = 1;
+ newp->sem = existing;
+ memcpy (newp->name, name, namelen);
+
+ /* Insert the new value. */
+ if (tsearch (newp, &__sem_mappings, __sem_search) != NULL)
+ /* Successful. */
+ result = existing;
+ else
+ /* Something went wrong while inserting the new
+ value. We fail completely. */
+ free (newp);
+ }
+ }
+
+ /* Release the lock. */
+ lll_unlock (__sem_mappings_lock);
+ }
+
+ if (result != existing && existing != SEM_FAILED)
+ {
+ /* Do not disturb errno. */
+ INTERNAL_SYSCALL_DECL (err);
+ INTERNAL_SYSCALL (munmap, err, 2, existing, sizeof (sem_t));
+ }
+
+ return result;
+}
+
+
sem_t *
sem_open (const char *name, int oflag, ...)
{
char *finalname;
- size_t namelen;
sem_t *result = SEM_FAILED;
int fd;
@@ -150,12 +245,12 @@ sem_open (const char *name, int oflag, ...)
__set_errno (EINVAL);
return SEM_FAILED;
}
- namelen = strlen (name);
+ size_t namelen = strlen (name) + 1;
/* Create the name of the final file. */
- finalname = (char *) alloca (mountpoint.dirlen + namelen + 1);
+ finalname = (char *) alloca (mountpoint.dirlen + namelen);
__mempcpy (__mempcpy (finalname, mountpoint.dir, mountpoint.dirlen),
- name, namelen + 1);
+ name, namelen);
/* If the semaphore object has to exist simply open it. */
if ((oflag & O_CREAT) == 0 || (oflag & O_EXCL) == 0)
@@ -167,15 +262,22 @@ sem_open (const char *name, int oflag, ...)
if (fd == -1)
{
/* If we are supposed to create the file try this next. */
- if ((oflag & O_CREAT) != 0)
+ if ((oflag & O_CREAT) != 0 && errno == ENOENT)
goto try_create;
/* Return. errno is already set. */
}
else
- /* Map the sem_t structure from the file. */
- result = (sem_t *) mmap (NULL, sizeof (sem_t), PROT_READ | PROT_WRITE,
- MAP_SHARED, fd, 0);
+ {
+ /* Check whether we already have this semaphore mapped. */
+ result = check_add_mapping (name, namelen, fd, SEM_FAILED);
+
+ /* Map the sem_t structure from the file. */
+ if (result == SEM_FAILED)
+ result = (sem_t *) mmap (NULL, sizeof (sem_t),
+ PROT_READ | PROT_WRITE, MAP_SHARED,
+ fd, 0);
+ }
}
else
{
@@ -200,14 +302,6 @@ sem_open (const char *name, int oflag, ...)
return SEM_FAILED;
}
- tmpfname = (char *) alloca (mountpoint.dirlen + 6 + 1);
- strcpy (__mempcpy (tmpfname, mountpoint.dir, mountpoint.dirlen),
- "XXXXXX");
-
- fd = mkstemp (tmpfname);
- if (fd == -1)
- return SEM_FAILED;
-
/* Create the initial file content. */
sem_t initsem;
@@ -218,10 +312,44 @@ sem_open (const char *name, int oflag, ...)
memset ((char *) &initsem + sizeof (struct sem), '\0',
sizeof (sem_t) - sizeof (struct sem));
+ tmpfname = (char *) alloca (mountpoint.dirlen + 6 + 1);
+ char *xxxxxx = __mempcpy (tmpfname, mountpoint.dir, mountpoint.dirlen);
+
+ int retries = 0;
+#define NRETRIES 50
+ while (1)
+ {
+ /* Add the suffix for mktemp. */
+ strcpy (xxxxxx, "XXXXXX");
+
+ /* We really want to use mktemp here. We cannot use mkstemp
+ since the file must be opened with a specific mode. The
+ mode cannot later be set since then we cannot apply the
+ file create mask. */
+ if (mktemp (tmpfname) == NULL)
+ return SEM_FAILED;
+
+ /* Open the file. Make sure we do not overwrite anything. */
+ fd = __libc_open (tmpfname, O_RDWR | O_CREAT | O_EXCL, mode);
+ if (fd == -1)
+ {
+ if (errno == EEXIST)
+ {
+ if (++retries < NRETRIES)
+ continue;
+
+ __set_errno (EAGAIN);
+ }
+
+ return SEM_FAILED;
+ }
+
+ /* We got a file. */
+ break;
+ }
+
if (TEMP_FAILURE_RETRY (__libc_write (fd, &initsem, sizeof (sem_t)))
== sizeof (sem_t)
- /* Adjust the permission. */
- && fchmod (fd, mode) == 0
/* Map the sem_t structure from the file. */
&& (result = (sem_t *) mmap (NULL, sizeof (sem_t),
PROT_READ | PROT_WRITE, MAP_SHARED,
@@ -249,6 +377,11 @@ sem_open (const char *name, int oflag, ...)
goto try_again;
}
}
+ else
+ /* Insert the mapping into the search tree. This also
+ determines whether another thread sneaked by and already
+ added such a mapping despite the fact that we created it. */
+ result = check_add_mapping (name, namelen, fd, result);
}
/* Now remove the temporary name. This should never fail. If
@@ -262,7 +395,11 @@ sem_open (const char *name, int oflag, ...)
/* We don't need the file descriptor anymore. */
if (fd != -1)
- (void) __libc_close (fd);
+ {
+ /* Do not disturb errno. */
+ INTERNAL_SYSCALL_DECL (err);
+ INTERNAL_SYSCALL (close, err, 1, fd);
+ }
return result;
}