strange return from os.mkdir

[zhiting zhu]

 OSv:

>>> import os

>>> os.makedirs("/tmp/lambda_11111")

>>> os.mkdir("/tmp/lambda_11111/out_0/")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: '/tmp/lambda_11111/out_0/'
>>> os.mkdir("/tmp/lambda_11111/out_0")
>>>

On the host:

>>> import os
>>> os.makedirs("/tmp/lambda_11111")
>>> os.mkdir("/tmp/lambda_11111/out_0/")
>>>

Why I can't put the / in the path? I'm using the same python

Python 3.6.8 (default, Oct  7 2019, 12:59:55)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

from Ubuntu 18.04 LTS.

Best,

Zhiting

[Waldek Kozaczuk]

Indeed this looks like a bug in vfs layer. Thanks for finding it :-)

Here is a patch that fixes it (needs unit tests). 

diff --git a/fs/vfs/main.cc b/fs/vfs/main.cc

index 7e028ffb..eca89556 100644

--- a/fs/vfs/main.cc

+++ b/fs/vfs/main.cc

@@ -825,7 +825,7 @@ mkdir(const char *pathname, mode_t mode)

     mode = apply_umask(mode);

 

     trace_vfs_mkdir(pathname, mode);

-    if ((error = task_conv(t, pathname, VWRITE, path)) != 0)

+    if ((error = task_conv_remove_trailing_slash(t, pathname, VWRITE, path)) != 0)

         goto out_errno;

 

     error = sys_mkdir(path, mode);

@@ -853,7 +853,7 @@ int rmdir(const char *pathname)

     error = ENOENT;

     if (pathname == nullptr)

         goto out_errno;

-    if ((error = task_conv(t, pathname, VWRITE, path)) != 0)

+    if ((error = task_conv_remove_trailing_slash(t, pathname, VWRITE, path)) != 0)

         goto out_errno;

 

     error = sys_rmdir(path);

@@ -977,7 +977,7 @@ int chdir(const char *pathname)

     if (pathname == nullptr)

         goto out_errno;

 

-    if ((error = task_conv(t, pathname, VREAD, path)) != 0)

+    if ((error = task_conv_remove_trailing_slash(t, pathname, VREAD, path)) != 0)

         goto out_errno;

 

     /* Check if directory exits */

diff --git a/fs/vfs/vfs.h b/fs/vfs/vfs.h

index d86ef957..38d2a2ab 100644

--- a/fs/vfs/vfs.h

+++ b/fs/vfs/vfs.h

@@ -135,7 +135,8 @@ int sys_fchmod(int fd, mode_t mode);

 

 int task_alloc(struct task **pt);

 int task_conv(struct task *t, const char *path, int mode, char *full);

-int path_conv(char *wd, const char *cpath, char *full);

+int task_conv_remove_trailing_slash(struct task *t, const char *path, int mode, char *full);

 

 //int sec_file_permission(task_t task, char *path, int mode);

 int sec_vnode_permission(char *path);

diff --git a/fs/vfs/vfs_lookup.cc b/fs/vfs/vfs_lookup.cc

index ad03fe25..4569061b 100644

--- a/fs/vfs/vfs_lookup.cc

+++ b/fs/vfs/vfs_lookup.cc

@@ -85,7 +85,7 @@ namei_follow_link(struct dentry *dp, char *node, char *name, char *fp, size_t mo

     } else {

         strlcpy(t.get(), p, PATH_MAX);

         strlcpy(node, fp, mountpoint_len + c + 1);

-        path_conv(node, lp, fp);

+        path_conv(node, lp, fp, false);

         strlcat(fp, t.get(), PATH_MAX);

     }

     node[0] = 0;

diff --git a/fs/vfs/vfs_task.cc b/fs/vfs/vfs_task.cc

index 332c460d..178740a0 100644

--- a/fs/vfs/vfs_task.cc

+++ b/fs/vfs/vfs_task.cc

@@ -65,7 +65,7 @@ task_alloc(struct task **pt)

  * @full: full path to be returned

  */

 int

-path_conv(char *wd, const char *cpath, char *full)

+path_conv(char *wd, const char *cpath, char *full, bool truncate_trailing_slash)

 {

  char path[PATH_MAX];

  char *src, *tgt, *p, *end;

@@ -129,6 +129,10 @@ path_conv(char *wd, const char *cpath, char *full)

  }

  src = p + 1;

  }

+ if (truncate_trailing_slash &&

+ tgt != full && *(tgt - 1) == '/' && tgt - 1 != full) {

+ tgt--;

+ }

  *tgt = '\0';

 

  return (0);

@@ -141,8 +145,8 @@ path_conv(char *wd, const char *cpath, char *full)

  * @full: full path to be returned

  * @acc: access mode

  */

-int

-task_conv(struct task *t, const char *cpath, int acc, char *full)

+static int

+_task_conv(struct task *t, const char *cpath, int acc, char *full, bool truncate_trailing_slash)

 {

        int rc;

 

@@ -150,7 +154,7 @@ task_conv(struct task *t, const char *cpath, int acc, char *full)

                return (EFAULT);

        }

 

-       rc = path_conv(t->t_cwd, cpath, full);

+       rc = path_conv(t->t_cwd, cpath, full, truncate_trailing_slash);

        if (rc != 0) {

                return (rc);

        }

@@ -159,6 +163,32 @@ task_conv(struct task *t, const char *cpath, int acc, char *full)

        return (0); //sec_file_permission(t->t_taskid, full, acc);

 }

 

+/*

+ * Convert to full path from the cwd of task and path.

+ * @t:    task structure

+ * @path: target path

+ * @full: full path to be returned

+ * @acc: access mode

+ */

+int

+task_conv(struct task *t, const char *cpath, int acc, char *full)

+{

+    return _task_conv(t, cpath, acc, full, false);

+}

+

+/*

+ * Convert to full path from the cwd of task and path. Remove any trailing slash.

+ * @t:    task structure

+ * @path: target path

+ * @full: full path to be returned

+ * @acc: access mode

+ */

+int

+task_conv_remove_trailing_slash(struct task *t, const char *cpath, int acc, char *full)

+{

+    return _task_conv(t, cpath, acc, full, true);

+}

+

 /*

  * Safe copying function that checks for overflow.

  */

I will send a proper patch with unit tests later. I changes VFS in critical places so it would be nice to review it.

Also I am not 100% it fixes all the cases. Note I have not simply made a fix in central path_conv() function as t would break many non-directory cases where trailing slash matters.