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-rw-r--r--libpod/lock/shm/shm_lock.c452
1 files changed, 452 insertions, 0 deletions
diff --git a/libpod/lock/shm/shm_lock.c b/libpod/lock/shm/shm_lock.c
new file mode 100644
index 000000000..4af58d857
--- /dev/null
+++ b/libpod/lock/shm/shm_lock.c
@@ -0,0 +1,452 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "shm_lock.h"
+
+// Compute the size of the SHM struct
+static size_t compute_shm_size(uint32_t num_bitmaps) {
+ return sizeof(shm_struct_t) + (num_bitmaps * sizeof(lock_group_t));
+}
+
+// Take the given mutex.
+// Handles exceptional conditions, including a mutex locked by a process that
+// died holding it.
+// Returns 0 on success, or positive errno on failure.
+static int take_mutex(pthread_mutex_t *mutex) {
+ int ret_code;
+
+ do {
+ ret_code = pthread_mutex_lock(mutex);
+ } while(ret_code == EAGAIN);
+
+ if (ret_code == EOWNERDEAD) {
+ // The previous owner of the mutex died while holding it
+ // Take it for ourselves
+ ret_code = pthread_mutex_consistent(mutex);
+ if (ret_code != 0) {
+ // Someone else may have gotten here first and marked the state consistent
+ // However, the mutex could also be invalid.
+ // Fail here instead of looping back to trying to lock the mutex.
+ return ret_code;
+ }
+ } else if (ret_code != 0) {
+ return ret_code;
+ }
+
+ return 0;
+}
+
+// Release the given mutex.
+// Returns 0 on success, or positive errno on failure.
+static int release_mutex(pthread_mutex_t *mutex) {
+ int ret_code;
+
+ do {
+ ret_code = pthread_mutex_unlock(mutex);
+ } while(ret_code == EAGAIN);
+
+ if (ret_code != 0) {
+ return ret_code;
+ }
+
+ return 0;
+}
+
+// Set up an SHM segment holding locks for libpod.
+// num_locks must not be 0.
+// Path is the path to the SHM segment. It must begin with a single / and
+// container no other / characters, and be at most 255 characters including
+// terminating NULL byte.
+// Returns a valid pointer on success or NULL on error.
+// If an error occurs, negative ERRNO values will be written to error_code.
+shm_struct_t *setup_lock_shm(char *path, uint32_t num_locks, int *error_code) {
+ int shm_fd, i, j, ret_code;
+ uint32_t num_bitmaps;
+ size_t shm_size;
+ shm_struct_t *shm;
+ pthread_mutexattr_t attr;
+
+ // If error_code doesn't point to anything, we can't reasonably return errors
+ // So fail immediately
+ if (error_code == NULL) {
+ return NULL;
+ }
+
+ // We need a nonzero number of locks
+ if (num_locks == 0) {
+ *error_code = -1 * EINVAL;
+ return NULL;
+ }
+
+ if (path == NULL) {
+ *error_code = -1 * EINVAL;
+ return NULL;
+ }
+
+ // Calculate the number of bitmaps required
+ num_bitmaps = num_locks / BITMAP_SIZE;
+ if (num_locks % BITMAP_SIZE != 0) {
+ // The actual number given is not an even multiple of our bitmap size
+ // So round up
+ num_bitmaps += 1;
+ }
+
+ // Calculate size of the shm segment
+ shm_size = compute_shm_size(num_bitmaps);
+
+ // Create a new SHM segment for us
+ shm_fd = shm_open(path, O_RDWR | O_CREAT | O_EXCL, 0600);
+ if (shm_fd < 0) {
+ *error_code = -1 * errno;
+ return NULL;
+ }
+
+ // Increase its size to what we need
+ ret_code = ftruncate(shm_fd, shm_size);
+ if (ret_code < 0) {
+ *error_code = -1 * errno;
+ goto CLEANUP_UNLINK;
+ }
+
+ // Map the shared memory in
+ shm = mmap(NULL, shm_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
+ if (shm == MAP_FAILED) {
+ *error_code = -1 * errno;
+ goto CLEANUP_UNLINK;
+ }
+
+ // We have successfully mapped the memory, now initialize the region
+ shm->magic = MAGIC;
+ shm->unused = 0;
+ shm->num_locks = num_bitmaps * BITMAP_SIZE;
+ shm->num_bitmaps = num_bitmaps;
+
+ // Create an initializer for our pthread mutexes
+ ret_code = pthread_mutexattr_init(&attr);
+ if (ret_code != 0) {
+ *error_code = -1 * ret_code;
+ goto CLEANUP_UNMAP;
+ }
+
+ // Set mutexes to pshared - multiprocess-safe
+ ret_code = pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
+ if (ret_code != 0) {
+ *error_code = -1 * ret_code;
+ goto CLEANUP_FREEATTR;
+ }
+
+ // Set mutexes to robust - if a process dies while holding a mutex, we'll get
+ // a special error code on the next attempt to lock it.
+ // This should prevent panicing processes from leaving the state unusable.
+ ret_code = pthread_mutexattr_setrobust(&attr, PTHREAD_MUTEX_ROBUST);
+ if (ret_code != 0) {
+ *error_code = -1 * ret_code;
+ goto CLEANUP_FREEATTR;
+ }
+
+ // Initialize the mutex that protects the bitmaps using the mutex attributes
+ ret_code = pthread_mutex_init(&(shm->segment_lock), &attr);
+ if (ret_code != 0) {
+ *error_code = -1 * ret_code;
+ goto CLEANUP_FREEATTR;
+ }
+
+ // Initialize all bitmaps to 0 initially
+ // And initialize all semaphores they use
+ for (i = 0; i < num_bitmaps; i++) {
+ shm->locks[i].bitmap = 0;
+ for (j = 0; j < BITMAP_SIZE; j++) {
+ // Initialize each mutex
+ ret_code = pthread_mutex_init(&(shm->locks[i].locks[j]), &attr);
+ if (ret_code != 0) {
+ *error_code = -1 * ret_code;
+ goto CLEANUP_FREEATTR;
+ }
+ }
+ }
+
+ // Close the file descriptor, we're done with it
+ // Ignore errors, it's ok if we leak a single FD and this should only run once
+ close(shm_fd);
+
+ // Destroy the pthread initializer attribute.
+ // Again, ignore errors, this will only run once and we might leak a tiny bit
+ // of memory at worst.
+ pthread_mutexattr_destroy(&attr);
+
+ return shm;
+
+ // Cleanup after an error
+ CLEANUP_FREEATTR:
+ pthread_mutexattr_destroy(&attr);
+ CLEANUP_UNMAP:
+ munmap(shm, shm_size);
+ CLEANUP_UNLINK:
+ close(shm_fd);
+ shm_unlink(path);
+ return NULL;
+}
+
+// Open an existing SHM segment holding libpod locks.
+// num_locks is the number of locks that will be configured in the SHM segment.
+// num_locks cannot be 0.
+// Path is the path to the SHM segment. It must begin with a single / and
+// container no other / characters, and be at most 255 characters including
+// terminating NULL byte.
+// Returns a valid pointer on success or NULL on error.
+// If an error occurs, negative ERRNO values will be written to error_code.
+shm_struct_t *open_lock_shm(char *path, uint32_t num_locks, int *error_code) {
+ int shm_fd;
+ shm_struct_t *shm;
+ size_t shm_size;
+ uint32_t num_bitmaps;
+
+ if (error_code == NULL) {
+ return NULL;
+ }
+
+ // We need a nonzero number of locks
+ if (num_locks == 0) {
+ *error_code = -1 * EINVAL;
+ return NULL;
+ }
+
+ if (path == NULL) {
+ *error_code = -1 * EINVAL;
+ return NULL;
+ }
+
+ // Calculate the number of bitmaps required
+ num_bitmaps = num_locks / BITMAP_SIZE;
+ if (num_locks % BITMAP_SIZE != 0) {
+ num_bitmaps += 1;
+ }
+
+ // Calculate size of the shm segment
+ shm_size = compute_shm_size(num_bitmaps);
+
+ shm_fd = shm_open(path, O_RDWR, 0600);
+ if (shm_fd < 0) {
+ *error_code = -1 * errno;
+ return NULL;
+ }
+
+ // Map the shared memory in
+ shm = mmap(NULL, shm_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
+ if (shm == MAP_FAILED) {
+ *error_code = -1 * errno;
+ }
+
+ // Ignore errors, it's ok if we leak a single FD since this only runs once
+ close(shm_fd);
+
+ // Check if we successfully mmap'd
+ if (shm == MAP_FAILED) {
+ return NULL;
+ }
+
+ // Need to check the SHM to see if it's actually our locks
+ if (shm->magic != MAGIC) {
+ *error_code = -1 * errno;
+ goto CLEANUP;
+ }
+ if (shm->num_locks != (num_bitmaps * BITMAP_SIZE)) {
+ *error_code = -1 * errno;
+ goto CLEANUP;
+ }
+
+ return shm;
+
+ CLEANUP:
+ munmap(shm, shm_size);
+ return NULL;
+}
+
+// Close an open SHM lock struct, unmapping the backing memory.
+// The given shm_struct_t will be rendered unusable as a result.
+// On success, 0 is returned. On failure, negative ERRNO values are returned.
+int32_t close_lock_shm(shm_struct_t *shm) {
+ int ret_code;
+ size_t shm_size;
+
+ // We can't unmap null...
+ if (shm == NULL) {
+ return -1 * EINVAL;
+ }
+
+ shm_size = compute_shm_size(shm->num_bitmaps);
+
+ ret_code = munmap(shm, shm_size);
+
+ if (ret_code != 0) {
+ return -1 * errno;
+ }
+
+ return 0;
+}
+
+// Allocate the first available semaphore
+// Returns a positive integer guaranteed to be less than UINT32_MAX on success,
+// or negative errno values on failure
+// On sucess, the returned integer is the number of the semaphore allocated
+int64_t allocate_semaphore(shm_struct_t *shm) {
+ int ret_code, i;
+ bitmap_t test_map;
+ int64_t sem_number, num_within_bitmap;
+
+ if (shm == NULL) {
+ return -1 * EINVAL;
+ }
+
+ // Lock the semaphore controlling access to our shared memory
+ ret_code = take_mutex(&(shm->segment_lock));
+ if (ret_code != 0) {
+ return -1 * ret_code;
+ }
+
+ // Loop through our bitmaps to search for one that is not full
+ for (i = 0; i < shm->num_bitmaps; i++) {
+ if (shm->locks[i].bitmap != 0xFFFFFFFF) {
+ test_map = 0x1;
+ num_within_bitmap = 0;
+ while (test_map != 0) {
+ if ((test_map & shm->locks[i].bitmap) == 0) {
+ // Compute the number of the semaphore we are allocating
+ sem_number = (BITMAP_SIZE * i) + num_within_bitmap;
+ // OR in the bitmap
+ shm->locks[i].bitmap = shm->locks[i].bitmap | test_map;
+
+ // Clear the mutex
+ ret_code = release_mutex(&(shm->segment_lock));
+ if (ret_code != 0) {
+ return -1 * ret_code;
+ }
+
+ // Return the semaphore we've allocated
+ return sem_number;
+ }
+ test_map = test_map << 1;
+ num_within_bitmap++;
+ }
+ // We should never fall through this loop
+ // TODO maybe an assert() here to panic if we do?
+ }
+ }
+
+ // Clear the mutex
+ ret_code = release_mutex(&(shm->segment_lock));
+ if (ret_code != 0) {
+ return -1 * ret_code;
+ }
+
+ // All bitmaps are full
+ // We have no available semaphores, report allocation failure
+ return -1 * ENOSPC;
+}
+
+// Deallocate a given semaphore
+// Returns 0 on success, negative ERRNO values on failure
+int32_t deallocate_semaphore(shm_struct_t *shm, uint32_t sem_index) {
+ bitmap_t test_map;
+ int bitmap_index, index_in_bitmap, ret_code, i;
+
+ if (shm == NULL) {
+ return -1 * EINVAL;
+ }
+
+ // Check if the lock index is valid
+ if (sem_index >= shm->num_locks) {
+ return -1 * EINVAL;
+ }
+
+ bitmap_index = sem_index / BITMAP_SIZE;
+ index_in_bitmap = sem_index % BITMAP_SIZE;
+
+ // This should never happen if the sem_index test above succeeded, but better
+ // safe than sorry
+ if (bitmap_index >= shm->num_bitmaps) {
+ return -1 * EFAULT;
+ }
+
+ test_map = 0x1 << index_in_bitmap;
+
+ // Lock the mutex controlling access to our shared memory
+ ret_code = take_mutex(&(shm->segment_lock));
+ if (ret_code != 0) {
+ return -1 * ret_code;
+ }
+
+ // Check if the semaphore is allocated
+ if ((test_map & shm->locks[bitmap_index].bitmap) == 0) {
+ ret_code = release_mutex(&(shm->segment_lock));
+ if (ret_code != 0) {
+ return -1 * ret_code;
+ }
+
+ return -1 * ENOENT;
+ }
+
+ // The semaphore is allocated, clear it
+ // Invert the bitmask we used to test to clear the bit
+ test_map = ~test_map;
+ shm->locks[bitmap_index].bitmap = shm->locks[bitmap_index].bitmap & test_map;
+
+ ret_code = release_mutex(&(shm->segment_lock));
+ if (ret_code != 0) {
+ return -1 * ret_code;
+ }
+
+ return 0;
+}
+
+// Lock a given semaphore
+// Does not check if the semaphore is allocated - this ensures that, even for
+// removed containers, we can still successfully lock to check status (and
+// subsequently realize they have been removed).
+// Returns 0 on success, -1 on failure
+int32_t lock_semaphore(shm_struct_t *shm, uint32_t sem_index) {
+ int bitmap_index, index_in_bitmap, ret_code;
+
+ if (shm == NULL) {
+ return -1 * EINVAL;
+ }
+
+ if (sem_index >= shm->num_locks) {
+ return -1 * EINVAL;
+ }
+
+ bitmap_index = sem_index / BITMAP_SIZE;
+ index_in_bitmap = sem_index % BITMAP_SIZE;
+
+ return -1 * take_mutex(&(shm->locks[bitmap_index].locks[index_in_bitmap]));
+}
+
+// Unlock a given semaphore
+// Does not check if the semaphore is allocated - this ensures that, even for
+// removed containers, we can still successfully lock to check status (and
+// subsequently realize they have been removed).
+// Returns 0 on success, -1 on failure
+int32_t unlock_semaphore(shm_struct_t *shm, uint32_t sem_index) {
+ int bitmap_index, index_in_bitmap, ret_code;
+
+ if (shm == NULL) {
+ return -1 * EINVAL;
+ }
+
+ if (sem_index >= shm->num_locks) {
+ return -1 * EINVAL;
+ }
+
+ bitmap_index = sem_index / BITMAP_SIZE;
+ index_in_bitmap = sem_index % BITMAP_SIZE;
+
+ return -1 * release_mutex(&(shm->locks[bitmap_index].locks[index_in_bitmap]));
+}