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Subject[patch] add file position info to proc
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Date
From: Miklos Szeredi <mszeredi@suse.cz>

This patch adds support for finding out the current file position,
open flags and possibly other info in the future.

These new entries are added:

/proc/PID/fdinfo/FD
/proc/PID/task/TID/fdinfo/FD

For each fd the information is provided in the following format:

pos: 1234
flags: 0100002
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
Index: linux/fs/proc/base.c
===================================================================
--- linux.orig/fs/proc/base.c 2007-03-24 19:00:48.000000000 +0100
+++ linux/fs/proc/base.c 2007-03-24 22:28:14.000000000 +0100
@@ -1199,7 +1199,10 @@ out:
return ~0U;
}

-static int proc_fd_link(struct inode *inode, struct dentry **dentry, struct vfsmount **mnt)
+#define PROC_FDINFO_MAX 64
+
+static int proc_fd_info(struct inode *inode, struct dentry **dentry,
+ struct vfsmount **mnt, char *info)
{
struct task_struct *task = get_proc_task(inode);
struct files_struct *files = NULL;
@@ -1218,8 +1221,16 @@ static int proc_fd_link(struct inode *in
spin_lock(&files->file_lock);
file = fcheck_files(files, fd);
if (file) {
- *mnt = mntget(file->f_path.mnt);
- *dentry = dget(file->f_path.dentry);
+ if (mnt)
+ *mnt = mntget(file->f_path.mnt);
+ if (dentry)
+ *dentry = dget(file->f_path.dentry);
+ if (info)
+ snprintf(info, PROC_FDINFO_MAX,
+ "pos:\t%lli\n"
+ "flags:\t0%o\n",
+ (long long) file->f_pos,
+ file->f_flags);
spin_unlock(&files->file_lock);
put_files_struct(files);
return 0;
@@ -1230,6 +1241,12 @@ static int proc_fd_link(struct inode *in
return -ENOENT;
}

+static int proc_fd_link(struct inode *inode, struct dentry **dentry,
+ struct vfsmount **mnt)
+{
+ return proc_fd_info(inode, dentry, mnt, NULL);
+}
+
static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
{
struct inode *inode = dentry->d_inode;
@@ -1325,7 +1342,9 @@ out_iput:
goto out;
}

-static struct dentry *proc_lookupfd(struct inode * dir, struct dentry * dentry, struct nameidata *nd)
+static struct dentry *proc_lookupfd_common(struct inode *dir,
+ struct dentry *dentry,
+ instantiate_t instantiate)
{
struct task_struct *task = get_proc_task(dir);
unsigned fd = name_to_int(dentry);
@@ -1336,23 +1355,15 @@ static struct dentry *proc_lookupfd(stru
if (fd == ~0U)
goto out;

- result = proc_fd_instantiate(dir, dentry, task, &fd);
+ result = instantiate(dir, dentry, task, &fd);
out:
put_task_struct(task);
out_no_task:
return result;
}

-static int proc_fd_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
- struct task_struct *task, int fd)
-{
- char name[PROC_NUMBUF];
- int len = snprintf(name, sizeof(name), "%d", fd);
- return proc_fill_cache(filp, dirent, filldir, name, len,
- proc_fd_instantiate, task, &fd);
-}
-
-static int proc_readfd(struct file * filp, void * dirent, filldir_t filldir)
+static int proc_readfd_common(struct file * filp, void * dirent,
+ filldir_t filldir, instantiate_t instantiate)
{
struct dentry *dentry = filp->f_path.dentry;
struct inode *inode = dentry->d_inode;
@@ -1388,12 +1399,17 @@ static int proc_readfd(struct file * fil
for (fd = filp->f_pos-2;
fd < fdt->max_fds;
fd++, filp->f_pos++) {
+ char name[PROC_NUMBUF];
+ int len;

if (!fcheck_files(files, fd))
continue;
rcu_read_unlock();

- if (proc_fd_fill_cache(filp, dirent, filldir, p, fd) < 0) {
+ len = snprintf(name, sizeof(name), "%d", fd);
+ if (proc_fill_cache(filp, dirent, filldir,
+ name, len, instantiate,
+ p, &fd) < 0) {
rcu_read_lock();
break;
}
@@ -1408,6 +1424,32 @@ out_no_task:
return retval;
}

+static struct dentry *proc_lookupfd(struct inode *dir, struct dentry *dentry,
+ struct nameidata *nd)
+{
+ return proc_lookupfd_common(dir, dentry, proc_fd_instantiate);
+}
+
+static int proc_readfd(struct file *filp, void *dirent, filldir_t filldir)
+{
+ return proc_readfd_common(filp, dirent, filldir, proc_fd_instantiate);
+}
+
+static ssize_t proc_fdinfo_read(struct file *file, char __user *buf,
+ size_t len, loff_t *ppos)
+{
+ char tmp[PROC_FDINFO_MAX];
+ int err = proc_fd_info(file->f_path.dentry->d_inode, NULL, NULL, tmp);
+ if (!err)
+ err = simple_read_from_buffer(buf, len, ppos, tmp, strlen(tmp));
+ return err;
+}
+
+const struct file_operations proc_fdinfo_file_operations = {
+ .open = nonseekable_open,
+ .read = proc_fdinfo_read,
+};
+
static const struct file_operations proc_fd_operations = {
.read = generic_read_dir,
.readdir = proc_readfd,
@@ -1421,6 +1463,58 @@ static const struct inode_operations pro
.setattr = proc_setattr,
};

+static struct dentry *proc_fdinfo_instantiate(struct inode *dir,
+ struct dentry *dentry, struct task_struct *task, void *ptr)
+{
+ unsigned fd = *(unsigned *)ptr;
+ struct inode *inode;
+ struct proc_inode *ei;
+ struct dentry *error = ERR_PTR(-ENOENT);
+
+ inode = proc_pid_make_inode(dir->i_sb, task);
+ if (!inode)
+ goto out;
+ ei = PROC_I(inode);
+ ei->fd = fd;
+ inode->i_mode = S_IFREG | S_IRUSR;
+ inode->i_fop = &proc_fdinfo_file_operations;
+ dentry->d_op = &tid_fd_dentry_operations;
+ d_add(dentry, inode);
+ /* Close the race of the process dying before we return the dentry */
+ if (tid_fd_revalidate(dentry, NULL))
+ error = NULL;
+
+ out:
+ return error;
+}
+
+static struct dentry *proc_lookupfdinfo(struct inode *dir,
+ struct dentry *dentry,
+ struct nameidata *nd)
+{
+ return proc_lookupfd_common(dir, dentry, proc_fdinfo_instantiate);
+}
+
+static int proc_readfdinfo(struct file *filp, void *dirent, filldir_t filldir)
+{
+ return proc_readfd_common(filp, dirent, filldir,
+ proc_fdinfo_instantiate);
+}
+
+static const struct file_operations proc_fdinfo_operations = {
+ .read = generic_read_dir,
+ .readdir = proc_readfdinfo,
+};
+
+/*
+ * proc directories can do almost nothing..
+ */
+static const struct inode_operations proc_fdinfo_inode_operations = {
+ .lookup = proc_lookupfdinfo,
+ .setattr = proc_setattr,
+};
+
+
static struct dentry *proc_pident_instantiate(struct inode *dir,
struct dentry *dentry, struct task_struct *task, void *ptr)
{
@@ -1831,6 +1925,7 @@ static const struct inode_operations pro
static struct pid_entry tgid_base_stuff[] = {
DIR("task", S_IRUGO|S_IXUGO, task),
DIR("fd", S_IRUSR|S_IXUSR, fd),
+ DIR("fdinfo", S_IRUSR|S_IXUSR, fdinfo),
INF("environ", S_IRUSR, pid_environ),
INF("auxv", S_IRUSR, pid_auxv),
INF("status", S_IRUGO, pid_status),
@@ -1983,7 +2078,7 @@ static struct dentry *proc_pid_instantia
inode->i_op = &proc_tgid_base_inode_operations;
inode->i_fop = &proc_tgid_base_operations;
inode->i_flags|=S_IMMUTABLE;
- inode->i_nlink = 4;
+ inode->i_nlink = 5;
#ifdef CONFIG_SECURITY
inode->i_nlink += 1;
#endif
@@ -2113,6 +2208,7 @@ out_no_task:
*/
static struct pid_entry tid_base_stuff[] = {
DIR("fd", S_IRUSR|S_IXUSR, fd),
+ DIR("fdinfo", S_IRUSR|S_IXUSR, fdinfo),
INF("environ", S_IRUSR, pid_environ),
INF("auxv", S_IRUSR, pid_auxv),
INF("status", S_IRUGO, pid_status),
@@ -2192,7 +2288,7 @@ static struct dentry *proc_task_instanti
inode->i_op = &proc_tid_base_inode_operations;
inode->i_fop = &proc_tid_base_operations;
inode->i_flags|=S_IMMUTABLE;
- inode->i_nlink = 3;
+ inode->i_nlink = 4;
#ifdef CONFIG_SECURITY
inode->i_nlink += 1;
#endif
-
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