Commit f57a19a7 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Linus Torvalds

ipc,shm: document new limits in the uapi header

This is useful in the future and allows users to better understand the
reasoning behind the changes.

Also use UL as we're dealing with it anyways.
Signed-off-by: default avatarDavidlohr Bueso <>
Cc: Michael Kerrisk <>
Cc: Manfred Spraul <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 060028ba
......@@ -8,17 +8,20 @@
* SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can
* be modified by sysctl.
* SHMMNI, SHMMAX and SHMALL are default upper limits which can be
* modified by sysctl. The SHMMAX and SHMALL values have been chosen to
* be as large possible without facilitating scenarios where userspace
* causes overflows when adjusting the limits via operations of the form
* "retrieve current limit; add X; update limit". It is therefore not
* advised to make SHMMAX and SHMALL any larger. These limits are
* suitable for both 32 and 64-bit systems.
#define SHMMIN 1 /* min shared seg size (bytes) */
#define SHMMNI 4096 /* max num of segs system wide */
#define SHMMAX (ULONG_MAX - (1L<<24)) /* max shared seg size (bytes) */
#define SHMALL (ULONG_MAX - (1L<<24)) /* max shm system wide (pages) */
#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
#define SHMALL (ULONG_MAX - (1UL << 24)) /* max shm system wide (pages) */
#define SHMSEG SHMMNI /* max shared segs per process */
/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct shmid_ds {
struct ipc_perm shm_perm; /* operation perms */
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