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]));
+}