[PATCH v2 6/6] posix/mmap: add mmap hooks for MAP_SHARED shms
Gedare Bloom
gedare at rtems.org
Thu Apr 13 20:22:34 UTC 2017
Updates #2859.
---
cpukit/posix/include/rtems/posix/mmanimpl.h | 2 +-
cpukit/posix/include/rtems/posix/shm.h | 30 ++++
cpukit/posix/src/mmap.c | 208 +++++++++++++++++-----------
cpukit/posix/src/munmap.c | 17 ++-
cpukit/posix/src/shmheap.c | 20 +++
cpukit/posix/src/shmwkspace.c | 17 +++
6 files changed, 203 insertions(+), 91 deletions(-)
diff --git a/cpukit/posix/include/rtems/posix/mmanimpl.h b/cpukit/posix/include/rtems/posix/mmanimpl.h
index eff20e2..bb33ac9 100644
--- a/cpukit/posix/include/rtems/posix/mmanimpl.h
+++ b/cpukit/posix/include/rtems/posix/mmanimpl.h
@@ -34,7 +34,7 @@ typedef struct mmap_mappings_s {
size_t len; /**< The length of memory mapped */
int flags; /**< The mapping flags */
rtems_libio_t *iop; /**< The mapped object's file descriptor pointer */
- bool is_shm; /**< True if mapping a shared memory object */
+ bool is_shared_shm; /**< True if MAP_SHARED of shared memory */
} mmap_mapping;
extern rtems_chain_control mmap_mappings;
diff --git a/cpukit/posix/include/rtems/posix/shm.h b/cpukit/posix/include/rtems/posix/shm.h
index dfdd58e..9284b39 100644
--- a/cpukit/posix/include/rtems/posix/shm.h
+++ b/cpukit/posix/include/rtems/posix/shm.h
@@ -91,6 +91,16 @@ struct POSIX_Shm_Object_operations {
* Returns the number of bytes read (copied) into @a buf.
*/
int ( *object_read ) ( POSIX_Shm_Object *shm_obj, void *buf, size_t count );
+
+ /**
+ * @brief Maps a shared memory object.
+ *
+ * Establishes a memory mapping between the shared memory object and the
+ * caller.
+ *
+ * Returns the mapped address of the object.
+ */
+ void * ( *object_mmap ) ( POSIX_Shm_Object *shm_obj, size_t len, int prot, off_t off);
};
/**
@@ -144,6 +154,16 @@ extern int _POSIX_Shm_Object_read_from_workspace(
);
/**
+ * @brief object_mmap operation for shm objects stored in RTEMS Workspace.
+ */
+extern void * _POSIX_Shm_Object_mmap_from_workspace(
+ POSIX_Shm_Object *shm_obj,
+ size_t len,
+ int prot,
+ off_t off
+);
+
+/**
* @brief object_create operation for shm objects stored in C program heap.
*/
extern int _POSIX_Shm_Object_create_from_heap(
@@ -173,6 +193,16 @@ extern int _POSIX_Shm_Object_read_from_heap(
size_t count
);
+/**
+ * @brief object_mmap operation for shm objects stored in C program heap.
+ */
+extern void * _POSIX_Shm_Object_mmap_from_heap(
+ POSIX_Shm_Object *shm_obj,
+ size_t len,
+ int prot,
+ off_t off
+);
+
/** @} */
#ifdef __cplusplus
diff --git a/cpukit/posix/src/mmap.c b/cpukit/posix/src/mmap.c
index b1d1653..74c8a33 100644
--- a/cpukit/posix/src/mmap.c
+++ b/cpukit/posix/src/mmap.c
@@ -24,7 +24,7 @@
#include "rtems/libio_.h"
-#include <rtems/posix/mmanimpl.h>
+#include <rtems/posix/mmanimpl.h>
#include <rtems/posix/shmimpl.h>
#define RTEMS_MUTEX_ATTRIBS \
@@ -107,13 +107,28 @@ bool mmap_mappings_lock_release(
return true;
}
-static void shm_mmap( rtems_libio_t *iop )
+/* Helper function only gets called for mmap mappings of shared memory objects
+ * with the MAP_SHARED flag.
+ */
+static void *shm_mmap( rtems_libio_t *iop, size_t len, int prot, off_t off)
{
POSIX_Shm_Control *shm = iop_to_shm( iop );
+ void *m;
_Objects_Allocator_lock();
- ++shm->reference_count;
+
+ m = (*shm->shm_object.ops->object_mmap)( &shm->shm_object, len, prot, off);
+ if ( m != NULL ) {
+ /* Keep a reference in the shared memory to prevent its removal. */
+ ++shm->reference_count;
+
+ /* Update atime */
+ _POSIX_Shm_Update_atime(shm);
+ }
+
_Objects_Allocator_unlock();
+
+ return m;
}
void *mmap(
@@ -124,12 +139,13 @@ void *mmap(
mmap_mapping *mapping;
ssize_t r;
rtems_libio_t *iop;
-
- /*
- * Clear errno.
- */
+ bool map_fixed;
+
+ map_fixed = (flags & MAP_FIXED) == MAP_FIXED;
+
+ /* Clear errno. */
errno = 0;
-
+
/*
* Get a stat of the file to get the dev + inode number and to make sure the
* fd is ok. The normal libio calls cannot be used because we need to return
@@ -141,8 +157,7 @@ void *mmap(
return MAP_FAILED;
}
- /* Sucessful fstat ensures we have a good file descriptor. Get the
- * associated iop for later. */
+ /* fstat ensures we have a good file descriptor. Hold on to iop. */
iop = rtems_libio_iop( fildes );
if ( len == 0 ) {
@@ -150,14 +165,12 @@ void *mmap(
return MAP_FAILED;
}
- /*
- * Check the type of file we have and make sure it is supported.
- */
+ /* Check the type of file we have and make sure it is supported. */
if ( S_ISDIR( sb.st_mode ) || S_ISLNK( sb.st_mode )) {
errno = ENODEV;
return MAP_FAILED;
}
-
+
/*
* We can provide read, write and execute because the memory in RTEMS does
* not normally have protections but we cannot hide access to memory.
@@ -166,7 +179,18 @@ void *mmap(
errno = ENOTSUP;
return MAP_FAILED;
}
-
+
+ /* Either MAP_SHARED or MAP_PRIVATE must be defined, but not both */
+ if ( (flags & MAP_SHARED) == MAP_SHARED ) {
+ if ( (flags & MAP_PRIVATE) == MAP_PRIVATE ) {
+ errno = EINVAL;
+ return MAP_FAILED;
+ }
+ } else if ( (flags & MAP_PRIVATE != MAP_PRIVATE) ) {
+ errno = EINVAL;
+ return MAP_FAILED;
+ }
+
/*
* We can not normally provide restriction of write access. Reject any
* attempt to map without write permission, since we are not able to
@@ -177,11 +201,9 @@ void *mmap(
return MAP_FAILED;
}
- /*
- * Check to see if the mapping is valid for a regular file.
- */
+ /* Check to see if the mapping is valid for a regular file. */
if ( S_ISREG( sb.st_mode )
- /* FIXME: Should this be using strict inequality comparisons? It would
+ /* FIXME: Should this be using strict inequality (>) comparisons? It would
* be valid to map a region exactly equal to the st_size, e.g. see below. */
&& (( off >= sb.st_size ) || (( off + len ) >= sb.st_size ))) {
errno = EOVERFLOW;
@@ -190,29 +212,92 @@ void *mmap(
/*
* Check to see if the mapping is valid for other file/object types.
+ * Does this satisfy for devices?
*/
if ( sb.st_size < off + len ) {
errno = ENXIO;
return MAP_FAILED;
}
+ /* Do not seek on character devices, pipes, sockets, or memory objects. */
+ if ( S_ISREG( sb.st_mode ) || S_ISBLK( sb.st_mode ) ) {
+ if ( lseek( fildes, off, SEEK_SET ) < 0 ) {
+ return MAP_FAILED;
+ }
+ }
+
+ /* Create the mapping */
+ mapping = malloc( sizeof( mmap_mapping ));
+ if ( !mapping ) {
+ errno = ENOMEM;
+ return NULL;
+ }
+ memset( mapping, 0, sizeof( mmap_mapping ));
+ mapping->len = len;
+ mapping->flags = flags;
+ mapping->iop = iop;
+
+ /*
+ * HACK: We should have a better generic way to distinguish between
+ * shm objects and other mmap'd files. We need to know at munmap time
+ * if the mapping is to a shared memory object in order to refcnt shms.
+ * We could do this by providing mmap in the file operations if needed.
+ */
+ if ( (MAP_PRIVATE == (flags & MAP_PRIVATE)) ||
+ S_ISREG( sb.st_mode ) || S_ISBLK( sb.st_mode ) ||
+ S_ISCHR( sb.st_mode ) || S_ISFIFO( sb.st_mode ) ||
+ S_ISSOCK( sb.st_mode ) ) {
+ mapping->is_shared_shm = false;
+ } else {
+ mapping->is_shared_shm = true;
+ }
+
/*
- * Obtain the mmap lock. Sets errno on failure.
+ * MAP_SHARED currently is only supported for shared memory objects.
*/
+ if ( (MAP_SHARED == (flags & MAP_SHARED)) && (mapping->is_shared_shm == false) ) {
+ free( mapping );
+ errno = ENOTSUP;
+ return MAP_FAILED;
+ }
+
+ if ( map_fixed ) {
+ mapping->addr = addr;
+ } else if ( MAP_PRIVATE == (flags & MAP_PRIVATE) ) {
+ /* private mappings of shared memory do not need special treatment. */
+ mapping->is_shared_shm = false;
+ mapping->addr = malloc( len );
+ if ( !mapping->addr ) {
+ free( mapping );
+ errno = ENOMEM;
+ return MAP_FAILED;
+ }
+ }
+
+ /* MAP_FIXED is not supported for shared memory objects with MAP_SHARED. */
+ if ( map_fixed && mapping->is_shared_shm ) {
+ free( mapping );
+ errno = ENOTSUP;
+ return MAP_FAILED;
+ }
+
+ /* Lock access to mmap_mappings. Sets errno on failure. */
if ( !mmap_mappings_lock_obtain( ) )
return MAP_FAILED;
- if (( flags & MAP_FIXED ) == MAP_FIXED ) {
+ if ( map_fixed ) {
rtems_chain_node* node = rtems_chain_first (&mmap_mappings);
while ( !rtems_chain_is_tail( &mmap_mappings, node )) {
/*
* If the map is fixed see if this address is already mapped. At this
* point in time if there is an overlap in the mappings we return an
- * error.
+ * error. POSIX allows us to also return successfully by unmapping
+ * the overlapping prior mappings.
*/
mapping = (mmap_mapping*) node;
if ( ( addr >= mapping->addr ) &&
( addr < ( mapping->addr + mapping->len )) ) {
+ free( mapping );
mmap_mappings_lock_release( );
errno = ENXIO;
return MAP_FAILED;
@@ -221,74 +306,29 @@ void *mmap(
}
}
- mapping = malloc( sizeof( mmap_mapping ));
- if ( !mapping ) {
- mmap_mappings_lock_release( );
- errno = ENOMEM;
- return NULL;
- }
-
- memset( mapping, 0, sizeof( mmap_mapping ));
-
- mapping->len = len;
- mapping->flags = flags;
- mapping->iop = iop;
-
- if (( flags & MAP_FIXED ) != MAP_FIXED ) {
- mapping->addr = malloc( len );
- if ( !mapping->addr ) {
- mmap_mappings_lock_release( );
- free( mapping );
- errno = ENOMEM;
- return MAP_FAILED;
- }
-
+ /* Populate the data */
+ if ( MAP_PRIVATE == (flags & MAP_PRIVATE) ) {
/*
- * Do not seek on character devices, pipes, sockets, or memory objects.
+ * Use read() for private mappings. This updates atime as needed.
+ * Changes to the underlying object will NOT be reflected in the mapping.
+ * The underlying object can be removed while the mapping exists.
*/
- if ( S_ISREG( sb.st_mode ) || S_ISBLK( sb.st_mode ) ) {
- if ( lseek( fildes, off, SEEK_SET ) < 0 ) {
- mmap_mappings_lock_release( );
+ r = read( fildes, mapping->addr, len );
+
+ if ( r != len ) {
+ mmap_mappings_lock_release( );
+ if ( !map_fixed ) {
free( mapping->addr );
- free( mapping );
- return MAP_FAILED;
}
+ free( mapping );
+ errno = ENXIO;
+ return MAP_FAILED;
}
+ } else if ( MAP_SHARED == (flags & MAP_SHARED) ) {
+ /* Currently only shm objects can be MAP_SHARED. */
+ mapping->addr = shm_mmap(iop, len, prot, off);
}
- /* read updates atime satisfying POSIX spec for mmap */
- r = read( fildes, mapping->addr, len );
-
- if ( r != len ) {
- mmap_mappings_lock_release( );
- free( mapping->addr );
- free( mapping );
- errno = ENXIO;
- return MAP_FAILED;
- }
-
- /* FIXME: should have a better generic way to handle differences between
- * shm objects and other mmap'd files. the best way is probably to add an
- * mmap/munmap handler to the file_operations table, or some other reasonable
- * OOP-like approach to discriminate the 'type' of mapping. */
- if ( S_ISREG( sb.st_mode ) || S_ISBLK( sb.st_mode ) ||
- S_ISCHR( sb.st_mode ) || S_ISFIFO( sb.st_mode ) ||
- S_ISSOCK( sb.st_mode ) ) {
- mapping->is_shm = false;
- } else {
- mapping->is_shm = true;
- shm_mmap(iop);
- }
-
- /* FIXME:
- * MAP_SHARED is not supported for regular files, and probably should be?
- * MAP_PRIVATE is not supported for shared memory objects, and should be?
- */
-
- /* FIXME: for a mapping with MAP_SHARED and PROT_WRITE the mtime/ctime
- * should be updated when there is a write reference to the mapped region.
- * How do we make this happen? */
-
/* add an extra reference to the file associated with fildes that
* is not removed by a subsequent close(). This reference shall be removed
* when there are no more mappings to the file. */
@@ -297,6 +337,6 @@ void *mmap(
rtems_chain_append( &mmap_mappings, &mapping->node );
mmap_mappings_lock_release( );
-
+
return mapping->addr;
}
diff --git a/cpukit/posix/src/munmap.c b/cpukit/posix/src/munmap.c
index b315034..588562f 100644
--- a/cpukit/posix/src/munmap.c
+++ b/cpukit/posix/src/munmap.c
@@ -18,12 +18,19 @@
#include <rtems/posix/mmanimpl.h>
#include <rtems/posix/shmimpl.h>
+static void shm_munmap( rtems_libio_t *iop )
+{
+ POSIX_Shm_Control *shm = iop_to_shm( iop );
+
+ /* decrement mmap's shm reference_count and maybe delete the object */
+ POSIX_Shm_Attempt_delete(shm);
+}
+
int munmap(void *addr, size_t len)
{
mmap_mapping *mapping;
rtems_chain_node *node;
uint32_t refcnt;
- POSIX_Shm_Control *shm;
/*
* Clear errno.
@@ -51,11 +58,9 @@ int munmap(void *addr, size_t len)
( addr < ( mapping->addr + mapping->len )) ) {
rtems_chain_extract( node );
/* FIXME: generally need a way to clean-up the backing object, but
- * currently it only matters for shm objects. */
- if ( mapping->is_shm == true ) {
- /* decrement mmap's shm reference_count and maybe delete the object */
- shm = iop_to_shm(mapping->iop);
- POSIX_Shm_Attempt_delete(shm);
+ * currently it only matters for MAP_SHARED shm objects. */
+ if ( mapping->is_shared_shm == true ) {
+ shm_munmap(mapping->iop);
}
refcnt = rtems_libio_decrement_mapping_refcnt(mapping->iop);
if ( refcnt == 0 ) {
diff --git a/cpukit/posix/src/shmheap.c b/cpukit/posix/src/shmheap.c
index 3449c15..47f5b47 100644
--- a/cpukit/posix/src/shmheap.c
+++ b/cpukit/posix/src/shmheap.c
@@ -70,6 +70,7 @@ int _POSIX_Shm_Object_resize_from_heap(
return err;
}
+/* This is identical to _POSIX_Shm_Object_read_from_wkspace */
int _POSIX_Shm_Object_read_from_heap(
POSIX_Shm_Object *shm_obj,
void *buf,
@@ -88,3 +89,22 @@ int _POSIX_Shm_Object_read_from_heap(
return count;
}
+/* This is identical to _POSIX_Shm_Object_mmap_from_wkspace */
+void * _POSIX_Shm_Object_mmap_from_heap(
+ POSIX_Shm_Object *shm_obj,
+ size_t len,
+ int prot,
+ off_t off
+)
+{
+ if ( shm_obj == NULL || shm_obj->handle == NULL )
+ return 0;
+
+ /* This is already checked by mmap. Maybe make it a debug assert? */
+ if ( shm_obj->size < len + off ) {
+ return NULL;
+ }
+
+ return &(shm_obj->handle[off]);
+}
+
diff --git a/cpukit/posix/src/shmwkspace.c b/cpukit/posix/src/shmwkspace.c
index 6d6cd21..926c14b 100644
--- a/cpukit/posix/src/shmwkspace.c
+++ b/cpukit/posix/src/shmwkspace.c
@@ -75,4 +75,21 @@ int _POSIX_Shm_Object_read_from_workspace(
return count;
}
+void * _POSIX_Shm_Object_mmap_from_wkspace(
+ POSIX_Shm_Object *shm_obj,
+ size_t len,
+ int prot,
+ off_t off
+)
+{
+ if ( shm_obj == NULL || shm_obj->handle == NULL )
+ return 0;
+
+ /* This is already checked by mmap. Maybe make it a debug assert? */
+ if ( shm_obj->size < len + off ) {
+ return NULL;
+ }
+
+ return &(shm_obj->handle[off]);
+}
--
2.7.4
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