[PATCH v4] block: report errno when flock fcntl fails

[David Edmondson]

When a call to fcntl(2) for the purpose of manipulating file locks
fails with an error other than EAGAIN or EACCES, report the error
returned by fcntl.

EAGAIN or EACCES are elided as they are considered to be common
failures, indicating that a conflicting lock is held by another
process.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
---
v3:
- Remove the now unnecessary updates to the test framework (Max).
- Elide the error detail for EAGAIN or EACCES when locking (Kevin,
  sort-of Max).
- Philippe and Vladimir sent Reviewed-by, but things have changed
  noticeably, so I didn't add them (dme).

v4:
- Really, really remove the unnecessary updates to the test framework.

 block/file-posix.c | 52 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 42 insertions(+), 10 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 00cdaaa2d4..c5142f7ffa 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -836,7 +836,13 @@ static int raw_apply_lock_bytes(BDRVRawState *s, int fd,
         if ((perm_lock_bits & bit) && !(locked_perm & bit)) {
             ret = qemu_lock_fd(fd, off, 1, false);
             if (ret) {
-                error_setg(errp, "Failed to lock byte %d", off);
+                int err = -ret;
+
+                if (err == EAGAIN || err == EACCES) {
+                    error_setg(errp, "Failed to lock byte %d", off);
+                } else {
+                    error_setg_errno(errp, err, "Failed to lock byte %d", off);
+                }
                 return ret;
             } else if (s) {
                 s->locked_perm |= bit;
@@ -844,7 +850,13 @@ static int raw_apply_lock_bytes(BDRVRawState *s, int fd,
         } else if (unlock && (locked_perm & bit) && !(perm_lock_bits & bit)) {
             ret = qemu_unlock_fd(fd, off, 1);
             if (ret) {
-                error_setg(errp, "Failed to unlock byte %d", off);
+                int err = -ret;
+
+                if (err == EAGAIN || err == EACCES) {
+                    error_setg(errp, "Failed to lock byte %d", off);
+                } else {
+                    error_setg_errno(errp, err, "Failed to lock byte %d", off);
+                }
                 return ret;
             } else if (s) {
                 s->locked_perm &= ~bit;
@@ -857,7 +869,13 @@ static int raw_apply_lock_bytes(BDRVRawState *s, int fd,
         if ((shared_perm_lock_bits & bit) && !(locked_shared_perm & bit)) {
             ret = qemu_lock_fd(fd, off, 1, false);
             if (ret) {
-                error_setg(errp, "Failed to lock byte %d", off);
+                int err = -ret;
+
+                if (err == EAGAIN || err == EACCES) {
+                    error_setg(errp, "Failed to lock byte %d", off);
+                } else {
+                    error_setg_errno(errp, err, "Failed to lock byte %d", off);
+                }
                 return ret;
             } else if (s) {
                 s->locked_shared_perm |= bit;
@@ -866,7 +884,7 @@ static int raw_apply_lock_bytes(BDRVRawState *s, int fd,
                    !(shared_perm_lock_bits & bit)) {
             ret = qemu_unlock_fd(fd, off, 1);
             if (ret) {
-                error_setg(errp, "Failed to unlock byte %d", off);
+                error_setg_errno(errp, -ret, "Failed to unlock byte %d", off);
                 return ret;
             } else if (s) {
                 s->locked_shared_perm &= ~bit;
@@ -890,9 +908,16 @@ static int raw_check_lock_bytes(int fd, uint64_t perm, 
uint64_t shared_perm,
             ret = qemu_lock_fd_test(fd, off, 1, true);
             if (ret) {
                 char *perm_name = bdrv_perm_names(p);
-                error_setg(errp,
-                           "Failed to get \"%s\" lock",
-                           perm_name);
+                int err = -ret;
+
+                if (err == EAGAIN || err == EACCES) {
+                    error_setg(errp, "Failed to get \"%s\" lock",
+                               perm_name);
+                } else {
+                    error_setg_errno(errp, err,
+                                     "Failed to get \"%s\" lock",
+                                     perm_name);
+                }
                 g_free(perm_name);
                 return ret;
             }
@@ -905,9 +930,16 @@ static int raw_check_lock_bytes(int fd, uint64_t perm, 
uint64_t shared_perm,
             ret = qemu_lock_fd_test(fd, off, 1, true);
             if (ret) {
                 char *perm_name = bdrv_perm_names(p);
-                error_setg(errp,
-                           "Failed to get shared \"%s\" lock",
-                           perm_name);
+                int err = -ret;
+
+                if (err == EAGAIN || err == EACCES) {
+                    error_setg(errp, "Failed to get shared \"%s\" lock",
+                               perm_name);
+                } else {
+                    error_setg_errno(errp, err,
+                                     "Failed to get shared \"%s\" lock",
+                                     perm_name);
+                }
                 g_free(perm_name);
                 return ret;
             }
-- 
2.29.2