[RFC][PATCH 3/3] [RFC][PATCH] Make /proc/pid/exe symlink changeable

Matt Helsley
2007-11-01T04:42:25Z

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This patch makes the /proc/<pid>|self/exe symlink writeable. This
functionality could be useful to potential checkpoint/restart implementations
restarting Java VMs, for example. Java uses this symlink to locate
JAVAHOME so any restarted Java program requires that /proc/self/exe points to
the jvm and not the restart exectuable.

Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
---
fs/proc/base.c | 37 ++++++++++++++++++++++++++++++++++++-
1 file changed, 36 insertions(+), 1 deletion(-)

Index: linux-2.6.23/fs/proc/base.c
===================================================================
--- linux-2.6.23.orig/fs/proc/base.c
+++ linux-2.6.23/fs/proc/base.c
@@ -930,10 +930,37 @@ static const struct file_operations proc
.release = single_release,
};

#endif

+static int proc_pid_exe_symlink(struct inode *inode, struct dentry *dentry,
+ const char *path)
+{
+ struct file *new_exe_file;
+ struct task_struct *task;
+ struct mm_struct *mm;
+ int error;
+
+ if (!proc_fd_access_allowed(dentry->d_inode))
+ return -EACCES;
+ task = get_proc_task(inode);
+ if (!task)
+ return -ENOENT;
+ mm = get_task_mm(task);
+ put_task_struct(task);
+ if (!mm)
+ return -ENOENT;
+ new_exe_file = open_exec(path);
+ error = PTR_ERR(new_exe_file);
+ if (!IS_ERR(error)) {
+ set_mm_exe_file(mm, new_exe_file);
+ error = 0;
+ }
+ mmput(mm);
+ return error;
+}
+
static int proc_exe_link(struct inode *inode, struct dentry **dentry,
struct vfsmount **mnt)
{
struct task_struct *task;
struct mm_struct *mm;
@@ -1027,10 +1054,16 @@ static const struct inode_operations pro
.readlink = proc_pid_readlink,
.follow_link = proc_pid_follow_link,
.setattr = proc_setattr,
};

+static const struct inode_operations proc_pid_exe_inode_operations = {
+ .readlink = proc_pid_readlink,
+ .follow_link = proc_pid_follow_link,
+ .symlink = proc_pid_exe_symlink,
+ .setattr = proc_setattr,
+};

/* building an inode */

static int task_dumpable(struct task_struct *task)
{
@@ -2087,11 +2120,13 @@ static const struct pid_entry tgid_base_
REG("numa_maps", S_IRUGO, numa_maps),
#endif
REG("mem", S_IRUSR|S_IWUSR, mem),
LNK("cwd", cwd),
LNK("root", root),
- LNK("exe", exe),
+ NOD("exe", (S_IFLNK|S_IRWXUGO),
+ &proc_pid_exe_inode_operations, NULL,
+ { .proc_get_link = &proc_exe_link }),
REG("mounts", S_IRUGO, mounts),
REG("mountstats", S_IRUSR, mountstats),
#ifdef CONFIG_MMU
REG("clear_refs", S_IWUSR, clear_refs),
REG("smaps", S_IRUGO, smaps),

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