[PATCH RFC] proc/pid/mem: implement SEEK_DATA and SEEK_HOLE
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_users))
+ return -ENXIO;
+ down_read(>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(>mmap_sem);
+ mmput(mm);
+ if (!vma)
+ return -ENXIO;
+ break;
default:
return -EINVAL;
}
--
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[PATCH RFC] proc/pid/mem: implement SEEK_DATA and SEEK_HOLE
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 koc...@gmail.com
---
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;
}
--
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the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
