On 08/20/2013 02:47 PM, Cyrill Gorcunov wrote:
> On Tue, Aug 20, 2013 at 01:41:40PM +0800, Chen Gang wrote:
>>
>>> sure you'll have to change shmem_show_mpol statement to return int code.
>>> Won't this be more short and convenient?
>>>
>>>
>>
>> Hmm... if return -ENOSPC, in common processing, it still need continue
>> (but need let outside know about the string truncation).
>>
>> So I still suggest to give more check for it.
>
> I still don't like adding additional code like
>
> + ret = mpol_to_str(buffer, sizeof(buffer), mpol);
> + if (ret < 0)
> + switch (ret) {
> + case -ENOSPC:
> + printk(KERN_WARNING
> + "in %s: string is truncated in mpol_to_str().\n",
> + __func__);
> + default:
> + printk(KERN_ERR
> + "in %s: call mpol_to_str() fail, errcode: %d. buffer: %p, size: %zu, pol: %p\n",
> + __func__, ret, buffer, sizeof(buffer), mpol);
> + return;
> + }
>
> this code is pretty neat for debugging purpose I think but in most case (if
> only I've not missed something obvious) it simply won't be the case.
>
For mpol_to_str(), it is for printing string, I suggest to fill buffer
as full as possible like another printing string functions, -ENOSPC is
not critical error, callers may can bear it, and still want to continue.
For 2 callers, I still suggest to process '-ENOSPC' and continue, it is
really not a critical error, they can continue.
For the 'default' error processing:
I still suggest to 'printk' in shmem_show_mpol(), because when failure occurs, it has no return value to mark the failure to upper caller.
Hmm... but for show_numa_map(), may remove the 'printk', only return the error code is OK. :-)
Thanks.
> Won't somthing like below do the same but with smaller code change?
> Note I've not even compiled it but it shows the idea.
> ---
> fs/proc/task_mmu.c | 4 +++-
> mm/shmem.c | 17 +++++++++--------
> 2 files changed, 12 insertions(+), 9 deletions(-)
>
> Index: linux-2.6.git/fs/proc/task_mmu.c
> ===================================================================
> --- linux-2.6.git.orig/fs/proc/task_mmu.c
> +++ linux-2.6.git/fs/proc/task_mmu.c
> @@ -1402,8 +1402,10 @@ static int show_numa_map(struct seq_file
> walk.mm = mm;
>
> pol = get_vma_policy(task, vma, vma->vm_start);
> - mpol_to_str(buffer, sizeof(buffer), pol);
> + n = mpol_to_str(buffer, sizeof(buffer), pol);
> mpol_cond_put(pol);
> + if (n < 0)
> + return n;
>
> seq_printf(m, "%08lx %s", vma->vm_start, buffer);
>
> Index: linux-2.6.git/mm/shmem.c
> ===================================================================
> --- linux-2.6.git.orig/mm/shmem.c
> +++ linux-2.6.git/mm/shmem.c
> @@ -883,16 +883,20 @@ redirty:
>
> #ifdef CONFIG_NUMA
> #ifdef CONFIG_TMPFS
> -static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
> +static int shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
> {
> char buffer[64];
> + int ret;
>
> if (!mpol || mpol->mode == MPOL_DEFAULT)
> - return; /* show nothing */
> + return 0; /* show nothing */
>
> - mpol_to_str(buffer, sizeof(buffer), mpol);
> + ret = mpol_to_str(buffer, sizeof(buffer), mpol);
> + if (ret < 0)
> + return ret;
>
> seq_printf(seq, ",mpol=%s", buffer);
> + return 0;
> }
>
> static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
> @@ -951,9 +955,7 @@ static struct page *shmem_alloc_page(gfp
> }
> #else /* !CONFIG_NUMA */
> #ifdef CONFIG_TMPFS
> -static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
> -{
> -}
> +static inline int shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol) { return 0; }
> #endif /* CONFIG_TMPFS */
>
> static inline struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
> @@ -2577,8 +2579,7 @@ static int shmem_show_options(struct seq
> if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
> seq_printf(seq, ",gid=%u",
> from_kgid_munged(&init_user_ns, sbinfo->gid));
> - shmem_show_mpol(seq, sbinfo->mpol);
> - return 0;
> + return shmem_show_mpol(seq, sbinfo->mpol);
> }
> #endif /* CONFIG_TMPFS */
>
>
>
--
Chen Gang
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