diff options
Diffstat (limited to 'libpod/lock')
| -rw-r--r-- | libpod/lock/locks.go | 167 | ||||
| -rw-r--r-- | libpod/lock/locks_test.go | 84 | ||||
| -rw-r--r-- | libpod/lock/shm_lock.c | 340 | ||||
| -rw-r--r-- | libpod/lock/shm_lock.h | 43 |
4 files changed, 634 insertions, 0 deletions
diff --git a/libpod/lock/locks.go b/libpod/lock/locks.go new file mode 100644 index 000000000..14da7d6a7 --- /dev/null +++ b/libpod/lock/locks.go @@ -0,0 +1,167 @@ +package lock + +// #cgo LDFLAGS: -lrt -lpthread +// #include "shm_lock.h" +// const uint32_t bitmap_size_c = BITMAP_SIZE; +import "C" + +import ( + "syscall" + + "github.com/pkg/errors" +) + +var ( + bitmapSize uint32 = uint32(C.bitmap_size_c) +) + +// SHMLocks is a struct enabling POSIX semaphore locking in a shared memory +// segment +type SHMLocks struct { + lockStruct *C.shm_struct_t + valid bool + maxLocks uint32 +} + +// CreateSHMLock sets up a shared-memory segment holding a given number of POSIX +// semaphores, and returns a struct that can be used to operate on those locks. +// numLocks must be a multiple of the lock bitmap size (by default, 32). +func CreateSHMLock(numLocks uint32) (*SHMLocks, error) { + if numLocks % bitmapSize != 0 { + return nil, errors.Wrapf(syscall.EINVAL, "number of locks must be a multiple of %d", C.bitmap_size_c) + } + + locks := new(SHMLocks) + + lockStruct := C.setup_lock_shm(C.uint32_t(numLocks)) + if lockStruct == nil { + // We got a null pointer, so something errored + return nil, errors.Wrapf(syscall.ENOENT, "error creating shared memory locks") + } + + locks.lockStruct = lockStruct + locks.maxLocks = numLocks + locks.valid = true + + return locks, nil +} + +// OpenSHMLock opens an existing shared-memory segment holding a given number of +// POSIX semaphores. numLocks must match the number of locks the shared memory +// segment was created with and be a multiple of the lock bitmap size (default +// 32) +func OpenSHMLock(numLocks uint32) (*SHMLocks, error) { + if numLocks % bitmapSize != 0 { + return nil, errors.Wrapf(syscall.EINVAL, "number of locks must be a multiple of %d", C.bitmap_size_c) + } + + locks := new(SHMLocks) + + lockStruct := C.open_lock_shm(C.uint32_t(numLocks)) + if lockStruct == nil { + // We got a null pointer, so something errored + return nil, errors.Wrapf(syscall.ENOENT, "error creating shared memory locks") + } + + locks.lockStruct = lockStruct + locks.maxLocks = numLocks + locks.valid = true + + return locks, nil +} + +// Close closes an existing shared-memory segment. +// The segment will be rendered unusable after closing. +// WARNING: If you Close() while there are still locks locked, these locks may +// fail to release, causing a program freeze. +// Close() is only intended to be used while testing the locks. +func (locks *SHMLocks) Close() error { + if !locks.valid { + return errors.Wrapf(syscall.EINVAL, "locks have already been closed") + } + + locks.valid = false + + retCode := C.close_lock_shm(locks.lockStruct) + if retCode < 0 { + // Negative errno returned + return syscall.Errno(-1 * retCode) + } + + return nil +} + +// AllocateSemaphore allocates a semaphore from a shared-memory segment for use +// by a container or pod. +// Returns the index of the semaphore that was allocated +func (locks *SHMLocks) AllocateSemaphore() (uint32, error) { + if !locks.valid { + return 0, errors.Wrapf(syscall.EINVAL, "locks have already been closed") + } + + retCode := C.allocate_semaphore(locks.lockStruct) + if retCode < 0 { + // Negative errno returned + return 0, syscall.Errno(-1 * retCode) + } + + return uint32(retCode), nil +} + +// DeallocateSemaphore frees a semaphore in a shared-memory segment for use by +// a container of pod +func (locks *SHMLocks) DeallocateSemaphore(sem uint32) error { + if !locks.valid { + return errors.Wrapf(syscall.EINVAL, "locks have already been closed") + } + + if sem > locks.maxLocks { + return errors.Wrapf(syscall.EINVAL, "given semaphore %d is higher than maximum locks count %d", sem, locks.maxLocks) + } + + retCode := C.deallocate_semaphore(locks.lockStruct, C.uint32_t(sem)) + if retCode < 0 { + // Negative errno returned + return syscall.Errno(-1 * retCode) + } + + return nil +} + +// LockSemaphore locks the given semaphore +func (locks *SHMLocks) LockSemaphore(sem uint32) error { + if !locks.valid { + return errors.Wrapf(syscall.EINVAL, "locks have already been closed") + } + + if sem > locks.maxLocks { + return errors.Wrapf(syscall.EINVAL, "given semaphore %d is higher than maximum locks count %d", sem, locks.maxLocks) + } + + retCode := C.lock_semaphore(locks.lockStruct, C.uint32_t(sem)) + if retCode < 0 { + // Negative errno returned + return syscall.Errno(-1 * retCode) + } + + return nil +} + +// UnlockSemaphore locks the given semaphore +func (locks *SHMLocks) UnlockSemaphore(sem uint32) error { + if !locks.valid { + return errors.Wrapf(syscall.EINVAL, "locks have already been closed") + } + + if sem > locks.maxLocks { + return errors.Wrapf(syscall.EINVAL, "given semaphore %d is higher than maximum locks count %d", sem, locks.maxLocks) + } + + retCode := C.unlock_semaphore(locks.lockStruct, C.uint32_t(sem)) + if retCode < 0 { + // Negative errno returned + return syscall.Errno(-1 * retCode) + } + + return nil +} diff --git a/libpod/lock/locks_test.go b/libpod/lock/locks_test.go new file mode 100644 index 000000000..b14d6e19a --- /dev/null +++ b/libpod/lock/locks_test.go @@ -0,0 +1,84 @@ +package lock + +import ( + "fmt" + "os" + "testing" + + "github.com/stretchr/testify/assert" + "github.com/stretchr/testify/require" +) + +// All tests here are in the same process, which somewhat limits their utility +// The big intent of this package it multiprocess locking, which is really hard +// to test without actually having multiple processes... +// We can at least verify that the locks work within the local process. + +// 4 * BITMAP_SIZE to ensure we have to traverse bitmaps +const numLocks = 128 + +// We need a test main to ensure that the SHM is created before the tests run +func TestMain(m *testing.M) { + shmLock, err := CreateSHMLock(numLocks) + if err != nil { + fmt.Fprintf(os.Stderr, "Error creating SHM for tests: %v\n", err) + os.Exit(-1) + } + + // Close the SHM - every subsequent test will reopen + if err := shmLock.Close(); err != nil { + fmt.Fprintf(os.Stderr, "Error closing SHM locks: %v\n", err) + os.Exit(-1) + } + + exitCode := m.Run() + + // We need to remove the SHM segment to clean up after ourselves + os.RemoveAll("/dev/shm/libpod_lock") + + os.Exit(exitCode) +} + + +func runLockTest(t *testing.T, testFunc func(*testing.T, *SHMLocks)) { + locks, err := OpenSHMLock(numLocks) + if err != nil { + t.Fatalf("Error opening locks: %v", err) + } + defer func() { + if err := locks.Close(); err != nil { + t.Fatalf("Error closing locks: %v", err) + } + }() + + success := t.Run("locks", func (t *testing.T) { + testFunc(t, locks) + }) + if !success { + t.Fail() + } +} + +// Test that creating an SHM with a bad size fails +func TestCreateNewSHMBadSize(t *testing.T) { + // Odd number, not a power of 2, should never be a word size on a system + _, err := CreateSHMLock(7) + assert.Error(t, err) +} + +// Test allocating - lock - unlock - deallocate cycle, single lock +func TestLockLifecycleSingleLock(t *testing.T) { + runLockTest(t, func(t *testing.T, locks *SHMLocks) { + sem, err := locks.AllocateSemaphore() + require.NoError(t, err) + + err = locks.LockSemaphore(sem) + assert.NoError(t, err) + + err = locks.UnlockSemaphore(sem) + assert.NoError(t, err) + + err = locks.DeallocateSemaphore(sem) + assert.NoError(t, err) + }) +} diff --git a/libpod/lock/shm_lock.c b/libpod/lock/shm_lock.c new file mode 100644 index 000000000..ab715891c --- /dev/null +++ b/libpod/lock/shm_lock.c @@ -0,0 +1,340 @@ +#include <errno.h> +#include <fcntl.h> +#include <semaphore.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 +size_t compute_shm_size(uint32_t num_bitmaps) { + return sizeof(shm_struct_t) + (num_bitmaps * sizeof(lock_group_t)); +} + +// Set up an SHM segment holding locks for libpod +// num_locks must be a multiple of BITMAP_SIZE (32 by default) +// Returns a valid pointer on success or NULL on error +shm_struct_t *setup_lock_shm(uint32_t num_locks) { + int shm_fd, i, j, ret_code; + uint32_t num_bitmaps; + size_t shm_size; + shm_struct_t *shm; + + // TODO maybe set errno so we can get errors back to libpod? + + // We need a nonzero number of locks + if (num_locks == 0) { + return NULL; + } + + // Calculate the number of bitmaps required + if (num_locks % BITMAP_SIZE != 0) { + // Number of locks not a multiple of BITMAP_SIZE + return NULL; + } + num_bitmaps = num_locks / BITMAP_SIZE; + + // Calculate size of the shm segment + shm_size = compute_shm_size(num_bitmaps); + + // Create a new SHM segment for us + shm_fd = shm_open(SHM_NAME, O_RDWR | O_CREAT | O_EXCL, 0600); + if (shm_fd < 0) { + return NULL; + } + + // Increase its size to what we need + ret_code = ftruncate(shm_fd, shm_size); + if (ret_code < 0) { + 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) { + goto CLEANUP_UNLINK; + } + + // We have successfully mapped the memory, now initialize the region + shm->magic = MAGIC; + shm->num_locks = num_locks; + shm->num_bitmaps = num_bitmaps; + + // Initialize the semaphore that protects the bitmaps + ret_code = sem_init(&(shm->segment_lock), 1, 1); + if (ret_code < 0) { + goto CLEANUP_UNMAP; + } + + // 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++) { + ret_code = sem_init(&(shm->locks[i].locks[j]), 1, 1); + if (ret_code < 0) { + goto CLEANUP_UNMAP; + } + } + } + + // 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); + + return shm; + + // Cleanup after an error + CLEANUP_UNMAP: + munmap(shm, shm_size); + CLEANUP_UNLINK: + close(shm_fd); + shm_unlink(SHM_NAME); + 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 must be a multiple of BITMAP_SIZE (32 by default) +// Returns a valid pointer on success or NULL on error +shm_struct_t *open_lock_shm(uint32_t num_locks) { + int shm_fd; + shm_struct_t *shm; + size_t shm_size; + uint32_t num_bitmaps; + + // We need a nonzero number of locks + if (num_locks == 0) { + return NULL; + } + + // Calculate the number of bitmaps required + if (num_locks % BITMAP_SIZE != 0) { + // Number of locks not a multiple of BITMAP_SIZE + return NULL; + } + num_bitmaps = num_locks / BITMAP_SIZE; + + // Calculate size of the shm segment + shm_size = compute_shm_size(num_bitmaps); + + shm_fd = shm_open(SHM_NAME, O_RDWR, 0600); + if (shm_fd < 0) { + return NULL; + } + + // Map the shared memory in + shm = mmap(NULL, shm_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0); + + // 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) { + goto CLEANUP; + } + if (shm->num_locks != num_locks) { + 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 + do { + ret_code = sem_wait(&(shm->segment_lock)); + } while(ret_code == EINTR); + if (ret_code != 0) { + return -1 * errno; + } + + // 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 semaphore + sem_post(&(shm->segment_lock)); + // 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? + } + } + + // Post to the semaphore to clear the lock + sem_post(&(shm->segment_lock)); + + // 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; + for (i = 0; i < index_in_bitmap; i++) { + test_map = test_map << 1; + } + + // Lock the semaphore controlling access to our shared memory + do { + ret_code = sem_wait(&(shm->segment_lock)); + } while(ret_code == EINTR); + if (ret_code != 0) { + return -1 * errno; + } + + // Check if the semaphore is allocated + if ((test_map & shm->locks[bitmap_index].bitmap) == 0) { + // Post to the semaphore to clear the lock + sem_post(&(shm->segment_lock)); + + 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; + + // Post to the semaphore to clear the lock + sem_post(&(shm->segment_lock)); + + 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; + + // Lock the semaphore controlling access to our shared memory + do { + ret_code = sem_wait(&(shm->locks[bitmap_index].locks[index_in_bitmap])); + } while(ret_code == EINTR); + if (ret_code != 0) { + return -1 * errno; + } + + return 0; +} + +// 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; + + 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; + + sem_post(&(shm->locks[bitmap_index].locks[index_in_bitmap])); + + return 0; +} diff --git a/libpod/lock/shm_lock.h b/libpod/lock/shm_lock.h new file mode 100644 index 000000000..6988789dd --- /dev/null +++ b/libpod/lock/shm_lock.h @@ -0,0 +1,43 @@ +#ifndef shm_locks_h_ +#define shm_locks_h_ + +#include <semaphore.h> +#include <stdint.h> + +// Magic number to ensure we open the right SHM segment +#define MAGIC 0xA5A5 + +// Name of the SHM +#define SHM_NAME "/libpod_lock" + +// Type for our bitmaps +typedef uint32_t bitmap_t; + +// bitmap size +#define BITMAP_SIZE (sizeof(bitmap_t) * 8) + +// Struct to hold a single bitmap and associated locks +typedef struct lock_group { + bitmap_t bitmap; + sem_t locks[BITMAP_SIZE]; +} lock_group_t; + +// Struct to hold our SHM locks +typedef struct shm_struct { + uint16_t magic; + sem_t segment_lock; + uint32_t num_bitmaps; + uint32_t num_locks; + lock_group_t locks[]; +} shm_struct_t; + +size_t compute_shm_size(uint32_t num_bitmaps); +shm_struct_t *setup_lock_shm(uint32_t num_locks); +shm_struct_t *open_lock_shm(uint32_t num_locks); +int32_t close_lock_shm(shm_struct_t *shm); +int64_t allocate_semaphore(shm_struct_t *shm); +int32_t deallocate_semaphore(shm_struct_t *shm, uint32_t sem_index); +int32_t lock_semaphore(shm_struct_t *shm, uint32_t sem_index); +int32_t unlock_semaphore(shm_struct_t *shm, uint32_t sem_index); + +#endif |