[Qemu-devel] [PATCH] Fix getgroups() syscall emulation

[Qemu-devel] [PATCH] Fix getgroups() syscall emulation

[Kirill A. Shutemov]

According to man page getgroups(2):

If size is zero, list is not modified, but the total number of
supplementary group IDs for the process is returned.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 linux-user/syscall.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 2abdc83..1f0ab34 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5242,6 +5242,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 
             grouplist = alloca(gidsetsize * sizeof(gid_t));
             ret = get_errno(getgroups(gidsetsize, grouplist));
+            if (gidsetsize == 0)
+                break;
             if (!is_error(ret)) {
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 2, 0);
                 if (!target_grouplist)
@@ -5392,6 +5394,8 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
 
             grouplist = alloca(gidsetsize * sizeof(gid_t));
             ret = get_errno(getgroups(gidsetsize, grouplist));
+            if (gidsetsize == 0)
+                break;
             if (!is_error(ret)) {
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 4, 0);
                 if (!target_grouplist) {
-- 
1.5.6.5.GIT

[Qemu-devel] [PATCH] Swap only altered elements of the grouplist

[Kirill A. Shutemov]

getgroups returns the number of supplementary group IDs is returned.
So it's unnessary to swap the entire array. It can dramatically speed up
the syscall: on recent Linux kernel NGROUPS_MAX=65536.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 linux-user/syscall.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 1f0ab34..9d76ade 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5248,7 +5248,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 2, 0);
                 if (!target_grouplist)
                     goto efault;
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap16(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 2);
             }
@@ -5402,7 +5402,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                     ret = -TARGET_EFAULT;
                     goto fail;
                 }
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap32(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 4);
             }
-- 
1.5.6.5.GIT

[Qemu-devel] [PATCH] Swap only altered elements of the grouplist

[Kirill A. Shutemov]

getgroups returns the number of supplementary group IDs is returned.
So it's unnessary to swap the entire array. It can dramatically speed up
the syscall: on recent Linux kernel NGROUPS_MAX=65536.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 linux-user/syscall.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 9d8542d..8112a56 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5248,7 +5248,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 2, 0);
                 if (!target_grouplist)
                     goto efault;
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap16(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 2);
             }
@@ -5402,7 +5402,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                     ret = -TARGET_EFAULT;
                     goto fail;
                 }
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap32(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 4);
             }
-- 
1.5.6.5.GIT

[Qemu-devel] [PATCH] Swap only altered elements of the grouplist

[Kirill A. Shutemov]

getgroups returns the number of supplementary group IDs is returned.
So it's unnessary to swap the entire array. It can dramatically speed up
the syscall: on recent Linux kernel NGROUPS_MAX=65536.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 linux-user/syscall.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 948ea3b..ba7cde1 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5253,7 +5253,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                 target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 2, 0);
                 if (!target_grouplist)
                     goto efault;
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap16(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 2);
             }
@@ -5407,7 +5407,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
                     ret = -TARGET_EFAULT;
                     goto fail;
                 }
-                for(i = 0;i < gidsetsize; i++)
+                for(i = 0;i < ret; i++)
                     target_grouplist[i] = tswap32(grouplist[i]);
                 unlock_user(target_grouplist, arg2, gidsetsize * 4);
             }
-- 
1.5.6.5.GIT

Re: [Qemu-devel] [PATCH] Swap only altered elements of the grouplist

[Riku Voipio]

On Thu, Sep 18, 2008 at 06:07:01PM +0300, Kirill A. Shutemov wrote:
> getgroups returns the number of supplementary group IDs is returned.
> So it's unnessary to swap the entire array. It can dramatically speed up
> the syscall: on recent Linux kernel NGROUPS_MAX=65536.

looks ok too.

> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> ---
>  linux-user/syscall.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 948ea3b..ba7cde1 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -5253,7 +5253,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>                  target_grouplist = lock_user(VERIFY_WRITE, arg2, gidsetsize * 2, 0);
>                  if (!target_grouplist)
>                      goto efault;
> -                for(i = 0;i < gidsetsize; i++)
> +                for(i = 0;i < ret; i++)
>                      target_grouplist[i] = tswap16(grouplist[i]);
>                  unlock_user(target_grouplist, arg2, gidsetsize * 2);
>              }
> @@ -5407,7 +5407,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>                      ret = -TARGET_EFAULT;
>                      goto fail;
>                  }
> -                for(i = 0;i < gidsetsize; i++)
> +                for(i = 0;i < ret; i++)
>                      target_grouplist[i] = tswap32(grouplist[i]);
>                  unlock_user(target_grouplist, arg2, gidsetsize * 4);
>              }
> -- 
> 1.5.6.5.GIT
> 
> 

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