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shm: Add mmap+memmove fallback if mremap() does not exist

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Some operating systems (e.g. FreeBSD) do not implement mremap.
In that case we can grow the mapping by trying to map adjacent memory.
If that fails we can fall back to creating a new larger mapping and
moving the old memory contents there.

Co-authored-by: Koop Mast <kwm@rainbow-runner.nl>
Signed-off-by: Alex Richardson <Alexander.Richardson@cl.cam.ac.uk>
This commit is contained in:
Alex Richardson 2021-03-15 22:25:52 +00:00 • committed by Alexander Richardson
parent 54b237a612
commit 5a981ee823
4 changed files with 74 additions and 9 deletions
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48
src/wayland-shm.c
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@ -45,6 +45,7 @@
#include <errno.h>
#include <fcntl.h>
#include "wayland-os.h"
#include "wayland-util.h"
#include "wayland-private.h"
#include "wayland-server.h"
@ -61,8 +62,12 @@ struct wl_shm_pool {
int internal_refcount;
int external_refcount;
char *data;
int32_t size;
int32_t new_size;
ssize_t size;
ssize_t new_size;
/* The following three fields are needed for mremap() emulation. */
int mmap_fd;
int mmap_flags;
int mmap_prot;
bool sigbus_is_impossible;
};
@ -90,6 +95,26 @@ struct wl_shm_sigbus_data {
int fallback_mapping_used;
};
static void *
shm_pool_grow_mapping(struct wl_shm_pool *pool)
{
void *data;
#ifdef MREMAP_MAYMOVE
data = mremap(pool->data, pool->size, pool->new_size, MREMAP_MAYMOVE);
#else
data = wl_os_mremap_maymove(pool->mmap_fd, pool->data, &pool->size,
pool->new_size, pool->mmap_prot,
pool->mmap_flags);
if (pool->size != 0) {
wl_resource_post_error(pool->resource,
WL_SHM_ERROR_INVALID_FD,
"leaked old mapping");
}
#endif
return data;
}
static void
shm_pool_finish_resize(struct wl_shm_pool *pool)
{
@ -98,7 +123,7 @@ shm_pool_finish_resize(struct wl_shm_pool *pool)
if (pool->size == pool->new_size)
return;
data = mremap(pool->data, pool->size, pool->new_size, MREMAP_MAYMOVE);
data = shm_pool_grow_mapping(pool);
if (data == MAP_FAILED) {
wl_resource_post_error(pool->resource,
WL_SHM_ERROR_INVALID_FD,
@ -127,6 +152,7 @@ shm_pool_unref(struct wl_shm_pool *pool, bool external)
return;
munmap(pool->data, pool->size);
close(pool->mmap_fd);
free(pool);
}
@ -274,6 +300,8 @@ shm_create_pool(struct wl_client *client, struct wl_resource *resource,
{
struct wl_shm_pool *pool;
int seals;
int prot;
int flags;
if (size <= 0) {
wl_resource_post_error(resource,
@ -301,17 +329,19 @@ shm_create_pool(struct wl_client *client, struct wl_resource *resource,
pool->external_refcount = 0;
pool->size = size;
pool->new_size = size;
pool->data = mmap(NULL, size,
PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
prot = PROT_READ | PROT_WRITE;
flags = MAP_SHARED;
pool->data = mmap(NULL, size, prot, flags, fd, 0);
if (pool->data == MAP_FAILED) {
wl_resource_post_error(resource,
WL_SHM_ERROR_INVALID_FD,
wl_resource_post_error(resource, WL_SHM_ERROR_INVALID_FD,
"failed mmap fd %d: %s", fd,
strerror(errno));
goto err_free;
}
close(fd);
/* We may need to keep the fd, prot and flags to emulate mremap(). */
pool->mmap_fd = fd;
pool->mmap_prot = prot;
pool->mmap_flags = flags;
pool->resource =
wl_resource_create(client, &wl_shm_pool_interface, 1, id);
if (!pool->resource) {