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Subject[RFC] fs, proc: Introduce the /proc/<pid>/map_files/ directory v2
From: Pavel Emelyanov <xemul@parallels.com>

This one behaves similarly to the /proc/<pid>/fd/ one - it contains symlinks
one for each mapping with file, the name of a symlink is vma->vm_start, the
target is the file. Opening a symlink results in a file that point exactly
to the same inode as them vma's one.

This thing is aimed to help checkpointing processes.

For example the ls -l of some arbitrary /proc/<pid>/map_files/

| lr-x------ 1 cyrill cyrill 64 Aug 9 15:25 0x3d73a00000 -> /lib64/ld-2.5.so
| lr-x------ 1 cyrill cyrill 64 Aug 9 15:25 0x3d73c1b000 -> /lib64/ld-2.5.so
| lr-x------ 1 cyrill cyrill 64 Aug 9 15:25 0x3d73c1c000 -> /lib64/ld-2.5.so
| lr-x------ 1 cyrill cyrill 64 Aug 9 15:25 0x3d73e00000 -> /lib64/libc-2.5.so
| lr-x------ 1 cyrill cyrill 64 Aug 9 15:25 0x3d73f4e000 -> /lib64/libc-2.5.so

v2:
- /proc/<pid>/mfd changed to /proc/<pid>/map_files
- find_vma helper is used instead of linear search
- routines are re-grouped
- .d_revalidate is set now

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
---
fs/proc/base.c | 191 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/proc_fs.h | 5 +
2 files changed, 195 insertions(+), 1 deletion(-)
Please review. This is a part of previous c/r patchset as well
but I guess it might be treated separately.

Objections, complains, comments are highly appreciated!

Index: linux-2.6.git/fs/proc/base.c
===================================================================
--- linux-2.6.git.orig/fs/proc/base.c
+++ linux-2.6.git/fs/proc/base.c
@@ -2170,6 +2170,196 @@ static const struct file_operations proc
.llseek = default_llseek,
};

+static const struct dentry_operations tid_map_files_dentry_operations = {
+ .d_revalidate = pid_revalidate,
+ .d_delete = pid_delete_dentry,
+};
+
+static int proc_map_files_get_link(struct inode *inode, struct path *path)
+{
+ struct task_struct *task;
+ struct vm_area_struct *vma;
+ struct mm_struct *mm;
+ unsigned long vm_start;
+ int rc = -ENOENT;
+
+ task = get_proc_task(inode);
+ if (!task)
+ goto out;
+
+ mm = get_task_mm(task);
+ put_task_struct(task);
+
+ if (!mm)
+ goto out;
+
+ vm_start = PROC_I(inode)->vm_start;
+
+ down_read(&mm->mmap_sem);
+ vma = find_vma(mm, vm_start);
+ if (vma && vma->vm_start == vm_start && vma->vm_file) {
+ *path = vma->vm_file->f_path;
+ path_get(path);
+ rc = 0;
+ }
+ up_read(&mm->mmap_sem);
+
+ mmput(mm);
+
+out:
+ return rc;
+}
+
+static struct dentry *
+proc_map_files_instantiate(struct inode *dir, struct dentry *dentry,
+ struct task_struct *task, const void *ptr)
+{
+ const struct vm_area_struct *vma = ptr;
+ struct file *file = vma->vm_file;
+ struct proc_inode *ei;
+ struct inode *inode;
+
+ if (!file)
+ return ERR_PTR(-ENOENT);
+
+ inode = proc_pid_make_inode(dir->i_sb, task);
+ if (!inode)
+ return ERR_PTR(-ENOENT);
+
+ ei = PROC_I(inode);
+ ei->vm_start = vma->vm_start;
+ ei->op.proc_get_link = proc_map_files_get_link;
+
+ inode->i_op = &proc_pid_link_inode_operations;
+ inode->i_size = 64;
+ inode->i_mode = S_IFLNK;
+
+ if (file->f_mode & FMODE_READ)
+ inode->i_mode |= S_IRUSR | S_IXUSR;
+ if (file->f_mode & FMODE_WRITE)
+ inode->i_mode |= S_IWUSR | S_IXUSR;
+
+ d_set_d_op(dentry, &tid_map_files_dentry_operations);
+ d_add(dentry, inode);
+
+ return NULL;
+}
+
+static struct dentry *proc_map_files_lookup(struct inode *dir,
+ struct dentry *dentry, struct nameidata *nd)
+{
+ struct task_struct *task;
+ unsigned long vm_start;
+ struct vm_area_struct *vma;
+ struct mm_struct *mm;
+ struct dentry *result;
+ char *endp;
+
+ result = ERR_PTR(-ENOENT);
+
+ task = get_proc_task(dir);
+ if (!task)
+ goto out_no_task;
+
+ vm_start = simple_strtoul(dentry->d_name.name, &endp, 16);
+ if (*endp != '\0')
+ goto out_no_mm;
+
+ mm = get_task_mm(task);
+ if (!mm)
+ goto out_no_mm;
+
+ down_read(&mm->mmap_sem);
+ vma = find_vma(mm, vm_start);
+ if (!vma || vma->vm_start != vm_start)
+ goto out_no_vma;
+ result = proc_map_files_instantiate(dir, dentry, task, vma);
+
+out_no_vma:
+ up_read(&mm->mmap_sem);
+ mmput(mm);
+out_no_mm:
+ put_task_struct(task);
+out_no_task:
+ return result;
+}
+
+static const struct inode_operations proc_map_files_inode_operations = {
+ .lookup = proc_map_files_lookup,
+ .setattr = proc_setattr,
+};
+
+static int proc_map_files_readdir(struct file *filp, void *dirent, filldir_t filldir)
+{
+ struct dentry *dentry = filp->f_path.dentry;
+ struct inode *inode = dentry->d_inode;
+ struct vm_area_struct *vma;
+ struct task_struct *task;
+ struct mm_struct *mm;
+ unsigned int vmai;
+ ino_t ino;
+ int ret;
+
+ ret = -ENOENT;
+ task = get_proc_task(inode);
+ if (!task)
+ goto out_no_task;
+
+ ret = -EPERM;
+ if (!ptrace_may_access(task, PTRACE_MODE_READ))
+ goto out;
+
+ ret = 0;
+ switch (filp->f_pos) {
+ case 0:
+ ino = inode->i_ino;
+ if (filldir(dirent, ".", 1, 0, ino, DT_DIR) < 0)
+ goto out;
+ filp->f_pos++;
+ case 1:
+ ino = parent_ino(dentry);
+ if (filldir(dirent, "..", 2, 1, ino, DT_DIR) < 0)
+ goto out;
+ filp->f_pos++;
+ default:
+ mm = get_task_mm(task);
+ if (!mm)
+ goto out;
+ down_read(&mm->mmap_sem);
+ for (vma = mm->mmap, vmai = 2; vma; vma = vma->vm_next) {
+ char name[2 + 16 + 1];
+ int len;
+
+ if (!vma->vm_file)
+ continue;
+
+ vmai++;
+ if (vmai < filp->f_pos)
+ continue;
+
+ filp->f_pos++;
+ len = snprintf(name, sizeof(name), "0x%lx", vma->vm_start);
+ if (proc_fill_cache(filp, dirent, filldir,
+ name, len, proc_map_files_instantiate,
+ task, vma) < 0)
+ break;
+ }
+ up_read(&mm->mmap_sem);
+ mmput(mm);
+ }
+
+out:
+ put_task_struct(task);
+out_no_task:
+ return ret;
+}
+
+static const struct file_operations proc_map_files_operations = {
+ .read = generic_read_dir,
+ .readdir = proc_map_files_readdir,
+ .llseek = default_llseek,
+};
+
/*
* /proc/pid/fd needs a special permission handler so that a process can still
* access /proc/self/fd after it has executed a setuid().
@@ -2785,6 +2975,7 @@ static const struct inode_operations pro
static const struct pid_entry tgid_base_stuff[] = {
DIR("task", S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
DIR("fd", S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
+ DIR("map_files", S_IRUSR|S_IXUSR, proc_map_files_inode_operations, proc_map_files_operations),
DIR("fdinfo", S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
DIR("ns", S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
#ifdef CONFIG_NET
Index: linux-2.6.git/include/linux/proc_fs.h
===================================================================
--- linux-2.6.git.orig/include/linux/proc_fs.h
+++ linux-2.6.git/include/linux/proc_fs.h
@@ -265,7 +265,10 @@ struct ctl_table;

struct proc_inode {
struct pid *pid;
- int fd;
+ union {
+ int fd;
+ unsigned long vm_start;
+ };
union proc_op op;
struct proc_dir_entry *pde;
struct ctl_table_header *sysctl;

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