diff options
| -rw-r--r-- | rfkill.c | 4 | ||||
| -rw-r--r-- | rfkill.h | 92 |
2 files changed, 81 insertions, 15 deletions
@@ -19,7 +19,7 @@ static void rfkill_event(void) { - struct rfkill_event event; + struct rfkill_event_ext event; struct timeval tv; struct pollfd p; ssize_t len; @@ -179,7 +179,7 @@ static struct rfkill_id rfkill_id_to_type(const char *s) static int rfkill_list(const char *param) { struct rfkill_id id = { .result = RFKILL_IS_INVALID }; - struct rfkill_event event; + struct rfkill_event_ext event; const char *name; ssize_t len; int fd; @@ -86,39 +86,105 @@ enum rfkill_hard_block_reasons { * @op: operation code * @hard: hard state (0/1) * @soft: soft state (0/1) + * + * Structure used for userspace communication on /dev/rfkill, + * used for events from the kernel and control to the kernel. + */ +struct rfkill_event { + __u32 idx; + __u8 type; + __u8 op; + __u8 soft; + __u8 hard; +} __attribute__((packed)); + +/** + * struct rfkill_event_ext - events for userspace on /dev/rfkill + * @idx: index of dev rfkill + * @type: type of the rfkill struct + * @op: operation code + * @hard: hard state (0/1) + * @soft: soft state (0/1) * @hard_block_reasons: valid if hard is set. One or several reasons from * &enum rfkill_hard_block_reasons. * * Structure used for userspace communication on /dev/rfkill, * used for events from the kernel and control to the kernel. + * + * See the extensibility docs below. */ -struct rfkill_event { +struct rfkill_event_ext { __u32 idx; __u8 type; __u8 op; __u8 soft; __u8 hard; + + /* + * older kernels will accept/send only up to this point, + * and if extended further up to any chunk marked below + */ + __u8 hard_block_reasons; } __attribute__((packed)); -/* - * We are planning to be backward and forward compatible with changes - * to the event struct, by adding new, optional, members at the end. - * When reading an event (whether the kernel from userspace or vice - * versa) we need to accept anything that's at least as large as the - * version 1 event size, but might be able to accept other sizes in - * the future. - * - * One exception is the kernel -- we already have two event sizes in - * that we've made the 'hard' member optional since our only option - * is to ignore it anyway. +/** + * DOC: Extensibility + * + * Originally, we had planned to allow backward and forward compatible + * changes by just adding fields at the end of the structure that are + * then not reported on older kernels on read(), and not written to by + * older kernels on write(), with the kernel reporting the size it did + * accept as the result. + * + * This would have allowed userspace to detect on read() and write() + * which kernel structure version it was dealing with, and if was just + * recompiled it would have gotten the new fields, but obviously not + * accessed them, but things should've continued to work. + * + * Unfortunately, while actually exercising this mechanism to add the + * hard block reasons field, we found that userspace (notably systemd) + * did all kinds of fun things not in line with this scheme: + * + * 1. treat the (expected) short writes as an error; + * 2. ask to read sizeof(struct rfkill_event) but then compare the + * actual return value to RFKILL_EVENT_SIZE_V1 and treat any + * mismatch as an error. + * + * As a consequence, just recompiling with a new struct version caused + * things to no longer work correctly on old and new kernels. + * + * Hence, we've rolled back &struct rfkill_event to the original version + * and added &struct rfkill_event_ext. This effectively reverts to the + * old behaviour for all userspace, unless it explicitly opts in to the + * rules outlined here by using the new &struct rfkill_event_ext. + * + * Additionally, some other userspace (bluez, g-s-d) was reading with a + * large size but as streaming reads rather than message-based, or with + * too strict checks for the returned size. So eventually, we completely + * reverted this, and extended messages need to be opted in to by using + * an ioctl: + * + * ioctl(fd, RFKILL_IOCTL_MAX_SIZE, sizeof(struct rfkill_event_ext)); + * + * Userspace using &struct rfkill_event_ext and the ioctl must adhere to + * the following rules: + * + * 1. accept short writes, optionally using them to detect that it's + * running on an older kernel; + * 2. accept short reads, knowing that this means it's running on an + * older kernel; + * 3. treat reads that are as long as requested as acceptable, not + * checking against RFKILL_EVENT_SIZE_V1 or such. */ -#define RFKILL_EVENT_SIZE_V1 8 +#define RFKILL_EVENT_SIZE_V1 sizeof(struct rfkill_event) /* ioctl for turning off rfkill-input (if present) */ #define RFKILL_IOC_MAGIC 'R' #define RFKILL_IOC_NOINPUT 1 #define RFKILL_IOCTL_NOINPUT _IO(RFKILL_IOC_MAGIC, RFKILL_IOC_NOINPUT) +#define RFKILL_IOC_MAX_SIZE 2 +#define RFKILL_IOCTL_MAX_SIZE _IOW(RFKILL_IOC_MAGIC, RFKILL_IOC_MAX_SIZE, __u32) /* and that's all userspace gets */ |