diff options
author | jhb <jhb@FreeBSD.org> | 2011-12-14 22:22:19 +0000 |
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committer | jhb <jhb@FreeBSD.org> | 2011-12-14 22:22:19 +0000 |
commit | 6d1299a388490b22f5d0619237868efafa3f3428 (patch) | |
tree | 99542359d8ee93e187d91428fb4d8a6e2d87bc67 /sys/kern/uipc_shm.c | |
parent | 83d1e21dd2a8af164c5792531d349adad212dee8 (diff) | |
download | FreeBSD-src-6d1299a388490b22f5d0619237868efafa3f3428.zip FreeBSD-src-6d1299a388490b22f5d0619237868efafa3f3428.tar.gz |
Add a helper API to allow in-kernel code to map portions of shared memory
objects created by shm_open(2) into the kernel's address space. This
provides a convenient way for creating shared memory buffers between
userland and the kernel without requiring custom character devices.
Diffstat (limited to 'sys/kern/uipc_shm.c')
-rw-r--r-- | sys/kern/uipc_shm.c | 119 |
1 files changed, 119 insertions, 0 deletions
diff --git a/sys/kern/uipc_shm.c b/sys/kern/uipc_shm.c index 3a639fb..d5a51e5 100644 --- a/sys/kern/uipc_shm.c +++ b/sys/kern/uipc_shm.c @@ -82,6 +82,7 @@ __FBSDID("$FreeBSD$"); #include <vm/vm_param.h> #include <vm/pmap.h> #include <vm/vm_map.h> +#include <vm/vm_kern.h> #include <vm/vm_object.h> #include <vm/vm_page.h> #include <vm/vm_pager.h> @@ -265,6 +266,14 @@ shm_dotruncate(struct shmfd *shmfd, off_t length) /* Are we shrinking? If so, trim the end. */ if (length < shmfd->shm_size) { + /* + * Disallow any requests to shrink the size if this + * object is mapped into the kernel. + */ + if (shmfd->shm_kmappings > 0) { + VM_OBJECT_UNLOCK(object); + return (EBUSY); + } delta = ptoa(object->size - nobjsize); /* Toss in memory pages. */ @@ -725,3 +734,113 @@ out: mtx_unlock(&shm_timestamp_lock); return (error); } + +/* + * Helper routines to allow the backing object of a shared memory file + * descriptor to be mapped in the kernel. + */ +int +shm_map(struct file *fp, size_t size, off_t offset, void **memp) +{ + struct shmfd *shmfd; + vm_offset_t kva, ofs; + vm_object_t obj; + int rv; + + if (fp->f_type != DTYPE_SHM) + return (EINVAL); + shmfd = fp->f_data; + obj = shmfd->shm_object; + VM_OBJECT_LOCK(obj); + /* + * XXXRW: This validation is probably insufficient, and subject to + * sign errors. It should be fixed. + */ + if (offset >= shmfd->shm_size || + offset + size > round_page(shmfd->shm_size)) { + VM_OBJECT_UNLOCK(obj); + return (EINVAL); + } + + shmfd->shm_kmappings++; + vm_object_reference_locked(obj); + VM_OBJECT_UNLOCK(obj); + + /* Map the object into the kernel_map and wire it. */ + kva = vm_map_min(kernel_map); + ofs = offset & PAGE_MASK; + offset = trunc_page(offset); + size = round_page(size + ofs); + rv = vm_map_find(kernel_map, obj, offset, &kva, size, + VMFS_ALIGNED_SPACE, VM_PROT_READ | VM_PROT_WRITE, + VM_PROT_READ | VM_PROT_WRITE, 0); + if (rv == KERN_SUCCESS) { + rv = vm_map_wire(kernel_map, kva, kva + size, + VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES); + if (rv == KERN_SUCCESS) { + *memp = (void *)(kva + ofs); + return (0); + } + vm_map_remove(kernel_map, kva, kva + size); + } else + vm_object_deallocate(obj); + + /* On failure, drop our mapping reference. */ + VM_OBJECT_LOCK(obj); + shmfd->shm_kmappings--; + VM_OBJECT_UNLOCK(obj); + + switch (rv) { + case KERN_INVALID_ADDRESS: + case KERN_NO_SPACE: + return (ENOMEM); + case KERN_PROTECTION_FAILURE: + return (EACCES); + default: + return (EINVAL); + } +} + +/* + * We require the caller to unmap the entire entry. This allows us to + * safely decrement shm_kmappings when a mapping is removed. + */ +int +shm_unmap(struct file *fp, void *mem, size_t size) +{ + struct shmfd *shmfd; + vm_map_entry_t entry; + vm_offset_t kva, ofs; + vm_object_t obj; + vm_pindex_t pindex; + vm_prot_t prot; + boolean_t wired; + vm_map_t map; + int rv; + + if (fp->f_type != DTYPE_SHM) + return (EINVAL); + shmfd = fp->f_data; + kva = (vm_offset_t)mem; + ofs = kva & PAGE_MASK; + kva = trunc_page(kva); + size = round_page(size + ofs); + map = kernel_map; + rv = vm_map_lookup(&map, kva, VM_PROT_READ | VM_PROT_WRITE, &entry, + &obj, &pindex, &prot, &wired); + if (rv != KERN_SUCCESS) + return (EINVAL); + if (entry->start != kva || entry->end != kva + size) { + vm_map_lookup_done(map, entry); + return (EINVAL); + } + vm_map_lookup_done(map, entry); + if (obj != shmfd->shm_object) + return (EINVAL); + vm_map_remove(map, kva, kva + size); + VM_OBJECT_LOCK(obj); + KASSERT(shmfd->shm_kmappings > 0, ("shm_unmap: object not mapped")); + shmfd->shm_kmappings--; + VM_OBJECT_UNLOCK(obj); + return (0); +} |