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[PATCH v7 02/10] ipc: "use key as id" functionality for resource get system call i [message #48470] Thu, 18 October 2012 10:22
Stanislav Kinsbursky is currently offline  Stanislav Kinsbursky
Messages: 683
Registered: October 2011
Senior Member
From: *parallels.com
This patch introduces new IPC resource get request flag IPC_PRESET, which
should be interpreted as a request to try to allocate IPC slot with number,
starting from value resented by key. IOW, kernel will try
allocate new segment in specified slot.

Note: if desired slot is not emply, then next free slot will be used.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
---
include/uapi/linux/ipc.h | 1 +
ipc/msg.c | 4 +++-
ipc/sem.c | 4 +++-
ipc/shm.c | 4 +++-
ipc/util.c | 18 +++++++++++++++---
ipc/util.h | 3 ++-
6 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/include/uapi/linux/ipc.h b/include/uapi/linux/ipc.h
index de08dd4..f5f52b6 100644
--- a/include/uapi/linux/ipc.h
+++ b/include/uapi/linux/ipc.h
@@ -24,6 +24,7 @@ struct ipc_perm
#define IPC_CREAT 00001000 /* create if key is nonexistent */
#define IPC_EXCL 00002000 /* fail if key exists */
#define IPC_NOWAIT 00004000 /* return error on wait */
+#define IPC_PRESET 00040000 /* use key as id */

/* these fields are used by the DIPC package so the kernel as standard
should avoid using them if possible */
diff --git a/ipc/msg.c b/ipc/msg.c
index 2f272fa..2f44946 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -190,6 +190,7 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)

msq->q_perm.mode = msgflg & S_IRWXUGO;
msq->q_perm.key = key;
+ msq->q_perm.id = (msgflg & IPC_PRESET) ? key : 0;

msq->q_perm.security = NULL;
retval = security_msg_queue_alloc(msq);
@@ -201,7 +202,8 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params)
/*
* ipc_addid() locks msq
*/
- id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni);
+ id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni,
+ msgflg & IPC_PRESET);
if (id < 0) {
security_msg_queue_free(msq);
ipc_rcu_putref(msq);
diff --git a/ipc/sem.c b/ipc/sem.c
index 58d31f1..10e9085 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -306,6 +306,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)

sma->sem_perm.mode = (semflg & S_IRWXUGO);
sma->sem_perm.key = key;
+ sma->sem_perm.id = (semflg & IPC_PRESET) ? key : 0;

sma->sem_perm.security = NULL;
retval = security_sem_alloc(sma);
@@ -314,7 +315,8 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
return retval;
}

- id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni);
+ id = ipc_addid(&sem_ids(ns), &sma->sem_perm, ns->sc_semmni,
+ semflg & IPC_PRESET);
if (id < 0) {
security_sem_free(sma);
ipc_rcu_putref(sma);
diff --git a/ipc/shm.c b/ipc/shm.c
index dff40c9..80b0046 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -480,6 +480,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)

shp->shm_perm.key = key;
shp->shm_perm.mode = (shmflg & S_IRWXUGO);
+ shp->shm_perm.id = (shmflg & IPC_PRESET) ? key : 0;
shp->mlock_user = NULL;

shp->shm_perm.security = NULL;
@@ -510,7 +511,8 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
if (IS_ERR(file))
goto no_file;

- id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni);
+ id = ipc_addid(&shm_ids(ns), &shp->shm_perm, ns->shm_ctlmni,
+ shmflg & IPC_PRESET);
if (id < 0) {
error = id;
goto no_id;
diff --git a/ipc/util.c b/ipc/util.c
index 72fd078..503946e 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -238,16 +238,22 @@ int ipc_get_maxid(struct ipc_ids *ids)
* @ids: IPC identifier set
* @new: new IPC permission set
* @size: limit for the number of used ids
+ * @preset: use passed new->id value as desired id
*
* Add an entry 'new' to the IPC ids idr. The permissions object is
* initialised and the first free entry is set up and the id assigned
* is returned. The 'new' entry is returned in a locked state on success.
* On failure the entry is not locked and a negative err-code is returned.
*
+ * If 'preset' is set, then passed new->id is desired to be set for new
+ * segment. And allocated id is equal to passed value, then ipc ids will
+ * left unchanged and new->seq will be updated to correspond specified id value.
+ *
* Called with ipc_ids.rw_mutex held as a writer.
*/

-int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
+int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size,
+ int preset)
{
kuid_t euid;
kgid_t egid;
@@ -264,7 +270,8 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
rcu_read_lock();
spin_lock(&new->lock);

- err = idr_get_new(&ids->ipcs_idr, new, &id);
+ err = idr_get_new_above(&ids->ipcs_idr, new,
+ ipcid_to_idx(new->id), &id);
if (err) {
spin_unlock(&new->lock);
rcu_read_unlock();
@@ -277,6 +284,11 @@ int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
new->cuid = new->uid = euid;
new->gid = new->cgid = egid;

+ if (preset && ipcid_to_idx(new->id) == id) {
+ new->seq = ipcid_to_seq(new->id);
+ return id;
+ }
+
new->seq = ids->seq++;
if(ids->seq > ids->seq_max)
ids->seq = 0;
@@ -736,7 +748,7 @@ struct kern_ipc_perm *ipc_lock_check(struct ipc_ids *ids, int id)
int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
struct ipc_ops *ops, struct ipc_params *params)
{
- if (params->key == IPC_PRIVATE)
+ if (params->key == IPC_PRIVATE && ((params->flg & IPC_PRESET) == 0))
return ipcget_new(ns, ids, ops, params);
else
return ipcget_public(ns, ids, ops, params);
diff --git a/ipc/util.h b/ipc/util.h
index c8fe2f7..3a9e558 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -92,9 +92,10 @@ void __init ipc_init_proc_interface(const char *path, const char *header,
#define IPC_SHM_IDS 2

#define ipcid_to_idx(id) ((id) % SEQ_MULTIPLIER)
+#define ipcid_to_seq(id) ((id) / SEQ_MULTIPLIER)

/* must be called with ids->rw_mutex acquired for writing */
-int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int);
+int ipc_addid(struct ipc_ids *, struct kern_ipc_perm *, int, int);

/* must be called with ids->rw_mutex acquired for reading */
int ipc_get_maxid(struct ipc_ids *);
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