[PATCH v1 03/14] mm/mshare: Add read for msharefs

Khalid Aziz
2022-04-11T16:08:34Z

Allocate a new mm to store shared page table. Add a read operation to
file created by mshare syscall to return the starting address and
size of region shared by the corresponding range. This information
is returned as struct mshare_info defined in include/uapi/linux/mman.h

Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
---
v1:
- Read returns struct instead of two unsigned long (suggested
by Mike Rapoport)

include/uapi/linux/mman.h | 5 +++
mm/mshare.c | 68 ++++++++++++++++++++++++++++++++++++---
2 files changed, 68 insertions(+), 5 deletions(-)

diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h
index f55bc680b5b0..56fe446e24b1 100644
--- a/include/uapi/linux/mman.h
+++ b/include/uapi/linux/mman.h
@@ -41,4 +41,9 @@
#define MAP_HUGE_2GB HUGETLB_FLAG_ENCODE_2GB
#define MAP_HUGE_16GB HUGETLB_FLAG_ENCODE_16GB

+struct mshare_info {
+ unsigned long start;
+ unsigned long size;
+};
+
#endif /* _UAPI_LINUX_MMAN_H */
diff --git a/mm/mshare.c b/mm/mshare.c
index ad695288d4bb..59e5d294e562 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -16,14 +16,39 @@
#include <linux/uaccess.h>
#include <linux/pseudo_fs.h>
#include <linux/fileattr.h>
+#include <linux/refcount.h>
+#include <linux/sched/mm.h>
#include <uapi/linux/magic.h>
#include <uapi/linux/limits.h>
+#include <uapi/linux/mman.h>
+
+struct mshare_data {
+ struct mm_struct *mm;
+ refcount_t refcnt;
+};

static struct super_block *msharefs_sb;

+static ssize_t
+mshare_read(struct kiocb *iocb, struct iov_iter *iov)
+{
+ struct mshare_data *info = iocb->ki_filp->private_data;
+ struct mm_struct *mm = info->mm;
+ size_t ret;
+ struct mshare_info m_info;
+
+ m_info.start = mm->mmap_base;
+ m_info.size = mm->task_size - mm->mmap_base;
+ ret = copy_to_iter(&m_info, sizeof(m_info), iov);
+ if (!ret)
+ return -EFAULT;
+ return ret;
+}
+
static const struct file_operations msharefs_file_operations = {
- .open = simple_open,
- .llseek = no_llseek,
+ .open = simple_open,
+ .read_iter = mshare_read,
+ .llseek = no_llseek,
};

static int
@@ -77,7 +102,12 @@ static struct inode

inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
inode->i_fop = &msharefs_file_operations;
- inode->i_size = 0;
+
+ /*
+ * A read from this file will return two unsigned long
+ */
+ inode->i_size = 2 * sizeof(unsigned long);
+
inode->i_uid = current_fsuid();
inode->i_gid = current_fsgid();
}
@@ -86,7 +116,8 @@ static struct inode
}

static int
-mshare_file_create(const char *name, unsigned long flags)
+mshare_file_create(const char *name, unsigned long flags,
+ struct mshare_data *info)
{
struct inode *inode;
struct dentry *root, *dentry;
@@ -98,6 +129,8 @@ mshare_file_create(const char *name, unsigned long flags)
if (IS_ERR(inode))
return PTR_ERR(inode);

+ inode->i_private = info;
+
dentry = msharefs_alloc_dentry(root, name);
if (IS_ERR(dentry)) {
err = PTR_ERR(dentry);
@@ -120,6 +153,8 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
unsigned long, len, int, oflag, mode_t, mode)
{
char mshare_name[NAME_MAX];
+ struct mshare_data *info;
+ struct mm_struct *mm;
int err;

/*
@@ -133,8 +168,31 @@ SYSCALL_DEFINE5(mshare, const char __user *, name, unsigned long, addr,
if (err)
goto err_out;

- err = mshare_file_create(mshare_name, oflag);
+ mm = mm_alloc();
+ if (!mm)
+ return -ENOMEM;
+ info = kzalloc(sizeof(*info), GFP_KERNEL);
+ if (!info) {
+ err = -ENOMEM;
+ goto err_relmm;
+ }
+ mm->mmap_base = addr;
+ mm->task_size = addr + len;
+ if (!mm->task_size)
+ mm->task_size--;
+ info->mm = mm;
+ refcount_set(&info->refcnt, 1);
+
+ err = mshare_file_create(mshare_name, oflag, info);
+ if (err)
+ goto err_relinfo;
+
+ return 0;

+err_relinfo:
+ kfree(info);
+err_relmm:
+ mmput(mm);
err_out:
return err;
}
--
2.32.0