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Re: [PATCH 21/22] Implement shmat(2) and shmdt(2)


From: Warner Losh
Subject: Re: [PATCH 21/22] Implement shmat(2) and shmdt(2)
Date: Sat, 19 Aug 2023 22:44:57 -0600



On Sat, Aug 19, 2023 at 3:49 AM Karim Taha <kariem.taha2.7@gmail.com> wrote:
From: Stacey Son <sson@FreeBSD.org>

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Karim Taha <kariem.taha2.7@gmail.com>
---
 bsd-user/bsd-mem.h            | 72 +++++++++++++++++++++++++++++++++++
 bsd-user/freebsd/os-syscall.c |  8 ++++
 2 files changed, 80 insertions(+)

diff --git a/bsd-user/bsd-mem.h b/bsd-user/bsd-mem.h
index 221ad76d8c..f737b94885 100644
--- a/bsd-user/bsd-mem.h
+++ b/bsd-user/bsd-mem.h
@@ -335,4 +335,76 @@ static inline abi_long do_bsd_shmctl(abi_long shmid, abi_long cmd,
     return ret;
 }

+/* shmat(2) */
+static inline abi_long do_bsd_shmat(int shmid, abi_ulong shmaddr, int shmflg)
+{
+    abi_ulong raddr;
+    abi_long ret;
+    void *host_raddr;
+    struct shmid_ds shm_info;
+    int i;
+
+    /* Find out the length of the shared memory segment. */
+    ret = get_errno(shmctl(shmid, IPC_STAT, &shm_info));
+    if (is_error(ret)) {
+        /* Can't get the length */
+        return ret;
+    }
+
+    mmap_lock();
+
+    if (shmaddr) {
+        host_raddr = shmat(shmid, (void *)g2h_untagged(shmaddr), shmflg);
+    } else {
+        abi_ulong mmap_start;
+
+        mmap_start = mmap_find_vma(0, shm_info.shm_segsz);
+
+        if (mmap_start == -1) {
+            errno = ENOMEM;
+            host_raddr = (void *)-1;
+        } else {
+            host_raddr = shmat(shmid, g2h_untagged(mmap_start),
+                shmflg); /* | SHM_REMAP XXX WHY? */

I was all set to hit reviewed by on this, but this has me curious. Kyle (or anybody else) do
you know the back story here. git blame is less than helpful.

Warner
 
+        }
+    }
+
+    if (host_raddr == (void *)-1) {
+        mmap_unlock();
+        return get_errno((long)host_raddr);
+    }
+    raddr = h2g((unsigned long)host_raddr);
+
+    page_set_flags(raddr, raddr + shm_info.shm_segsz,
+        PAGE_VALID | PAGE_READ | ((shmflg & SHM_RDONLY) ? 0 : PAGE_WRITE));
+
+    for (i = 0; i < N_BSD_SHM_REGIONS; i++) {
+        if (bsd_shm_regions[i].start == 0) {
+            bsd_shm_regions[i].start = raddr;
+            bsd_shm_regions[i].size = shm_info.shm_segsz;
+            break;
+        }
+    }
+
+    mmap_unlock();
+    return raddr;
+}
+
+/* shmdt(2) */
+static inline abi_long do_bsd_shmdt(abi_ulong shmaddr)
+{
+    int i;
+
+    for (i = 0; i < N_BSD_SHM_REGIONS; ++i) {
+        if (bsd_shm_regions[i].start == shmaddr) {
+            bsd_shm_regions[i].start = 0;
+            page_set_flags(shmaddr,
+                shmaddr + bsd_shm_regions[i].size, 0);
+            break;
+        }
+    }
+
+    return get_errno(shmdt(g2h_untagged(shmaddr)));
+}
+
 #endif /* BSD_USER_BSD_MEM_H */
diff --git a/bsd-user/freebsd/os-syscall.c b/bsd-user/freebsd/os-syscall.c
index 9681c65ce9..f76bc1eb38 100644
--- a/bsd-user/freebsd/os-syscall.c
+++ b/bsd-user/freebsd/os-syscall.c
@@ -559,6 +559,14 @@ static abi_long freebsd_syscall(void *cpu_env, int num, abi_long arg1,
         ret = do_bsd_shmctl(arg1, arg2, arg3);
         break;

+    case TARGET_FREEBSD_NR_shmat: /* shmat(2) */
+        ret = do_bsd_shmat(arg1, arg2, arg3);
+        break;
+
+    case TARGET_FREEBSD_NR_shmdt: /* shmdt(2) */
+        ret = do_bsd_shmdt(arg1);
+        break;
+
         /*
          * Misc
          */
--
2.40.0


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