From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751258AbaEXNum (ORCPT ); Sat, 24 May 2014 09:50:42 -0400 Received: from mail-lb0-f177.google.com ([209.85.217.177]:35741 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750748AbaEXNul (ORCPT ); Sat, 24 May 2014 09:50:41 -0400 Subject: [PATCH RFC] proc/pid/mem: implement SEEK_DATA and SEEK_HOLE From: Konstantin Khlebnikov To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Sat, 24 May 2014 17:50:35 +0400 Message-ID: <20140524135035.32281.93663.stgit@zurg> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org lseek(fd, addr, SEEK_DATA) adjust file offset to the start address of next VMA, or to addr if this address is allocated. lseek(fd, addr, SEEK_HOLE) adjust file offset to the end address of VMA which addr belongs to, or to addr itself if there is hole. This way SEEK_HOLE reports a virtual zero-length hole between each contiguous VMAs. This hack seems completely legit and allows to simplify implementation (there is no function for finding next hole in VMAs' tree, walking along ->vm_next might be expensive) This also gives more information about layout. Signed-off-by: Konstantin Khlebnikov --- I have no practical use for this, just found this interesting. --- fs/proc/base.c | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 2d696b0..aba4b47 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -769,13 +769,40 @@ static ssize_t mem_write(struct file *file, const char __user *buf, loff_t mem_lseek(struct file *file, loff_t offset, int orig) { + struct mm_struct *mm = file->private_data; + struct vm_area_struct *vma; + switch (orig) { - case 0: + case SEEK_SET: file->f_pos = offset; break; - case 1: + case SEEK_CUR: file->f_pos += offset; break; + case SEEK_DATA: + case SEEK_HOLE: + if (!mm || !atomic_inc_not_zero(&mm->mm_users)) + return -ENXIO; + down_read(&mm->mmap_sem); + vma = find_vma(mm, offset); + if (vma) { + if (orig == SEEK_DATA) { + if (offset >= vma->vm_start) + file->f_pos = offset; + else + file->f_pos = vma->vm_start; + } else { + if (offset < vma->vm_start) + file->f_pos = offset; + else + file->f_pos = vma->vm_end; + } + } + up_read(&mm->mmap_sem); + mmput(mm); + if (!vma) + return -ENXIO; + break; default: return -EINVAL; }