vim-patch:9.0.1962: No support for writing extended attributes

Problem:  No support for writing extended attributes
Solution: Add extended attribute support for linux

It's been a long standing issue, that if you write a file with extended
attributes and backupcopy is set to no, the file will loose the extended
attributes.

So this patch adds support for retrieving the extended attributes and
copying it to the new file. It currently only works on linux, mainly
because I don't know the different APIs for other systems (BSD, MacOSX and
Solaris).  On linux, this should be supported since Kernel 2.4 or
something, so this should be pretty safe to use now.

Enable the extended attribute support with normal builds.

I also added it explicitly to the :version output as well as make it
able to check using `:echo has("xattr")`, to have users easily check
that this is available.

In contrast to the similar support for SELINUX and SMACK support (which
also internally uses extended attributes), I have made this a FEAT_XATTR
define, instead of the similar HAVE_XATTR.

Add a test and change CI to include relevant packages so that CI can
test that extended attributes are correctly written.

closes: vim/vim#306
closes: vim/vim#13203

https://github.com/vim/vim/commit/e085dfda5d8dde064b0332464040959479696d1c

Co-authored-by: Christian Brabandt <cb@256bit.org>

3 files changed, 111 insertions, 1 deletions

diff --git a/src/nvim/bufwrite.c b/src/nvim/bufwrite.c
index 40b95e5790..db813a3ae1 100644
--- a/src/nvim/bufwrite.c
+++ b/src/nvim/bufwrite.c
@@ -913,6 +913,9 @@ static int buf_write_make_backup(char *fname, bool append, FileInfo *file_info_o
             && os_chown(*backupp, (uv_uid_t)-1, (uv_gid_t)file_info_old->stat.st_gid) != 0) {
           os_setperm(*backupp, ((int)perm & 0707) | (((int)perm & 07) << 3));
         }
+# ifdef HAVE_XATTR
+        os_copy_xattr(fname, *backupp);
+# endif
 #endif
 
         // copy the file
@@ -929,6 +932,9 @@ static int buf_write_make_backup(char *fname, bool append, FileInfo *file_info_o
                         (double)file_info_old->stat.st_mtim.tv_sec);
 #endif
         os_set_acl(*backupp, acl);
+#ifdef HAVE_XATTR
+        os_copy_xattr(fname, *backupp);
+#endif
         *err = set_err(NULL);
         break;
       }
@@ -1634,6 +1640,12 @@ restore_backup:
       end = 0;
     }
 
+    if (!backup_copy) {
+#ifdef HAVE_XATTR
+      os_copy_xattr(backup, wfname);
+#endif
+    }
+
 #ifdef UNIX
     // When creating a new file, set its owner/group to that of the original
     // file.  Get the new device and inode number.
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 710d9c73a5..5bfce7c272 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -3171,6 +3171,9 @@ static void f_has(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     "windows",
     "winaltkeys",
     "writebackup",
+#ifdef HAVE_XATTR
+    "xattr",
+#endif
     "nvim",
   };
 
diff --git a/src/nvim/os/fs.c b/src/nvim/os/fs.c
index 77c4766419..3efb575039 100644
--- a/src/nvim/os/fs.c
+++ b/src/nvim/os/fs.c
@@ -18,6 +18,8 @@
 # include <shlobj.h>
 #endif
 
+#include "auto/config.h"
+
 #if defined(HAVE_ACL)
 # ifdef HAVE_SYS_ACL_H
 #  include <sys/acl.h>
@@ -27,7 +29,11 @@
 # endif
 #endif
 
-#include "auto/config.h"
+#ifdef HAVE_XATTR
+# include <attr/xattr.h>
+# define XATTR_VAL_LEN 1024
+#endif
+
 #include "nvim/ascii.h"
 #include "nvim/gettext.h"
 #include "nvim/globals.h"
@@ -55,6 +61,17 @@
 # include "os/fs.c.generated.h"
 #endif
 
+#ifdef HAVE_XATTR
+static const char e_xattr_erange[]
+  = N_("E1506: Buffer too small to copy xattr value or key");
+static const char e_xattr_enotsup[]
+  = N_("E1507: Extended attributes are not supported by the filesystem");
+static const char e_xattr_e2big[]
+  = N_("E1508: size of the extended attribute value is larger than the maximum size allowed");
+static const char e_xattr_other[]
+  = N_("E1509: error occured when reading or writing extended attribute");
+#endif
+
 struct iovec;
 
 #define RUN_UV_FS_FUNC(ret, func, ...) \
@@ -743,6 +760,84 @@ int os_setperm(const char *const name, int perm)
   return (r == kLibuvSuccess ? OK : FAIL);
 }
 
+#ifdef HAVE_XATTR
+/// Copy extended attributes from_file to to_file
+void os_copy_xattr(const char *from_file, const char *to_file)
+{
+  if (from_file == NULL) {
+    return;
+  }
+
+  // get the length of the extended attributes
+  ssize_t size = listxattr((char *)from_file, NULL, 0);
+  // not supported or no attributes to copy
+  if (errno == ENOTSUP || size <= 0) {
+    return;
+  }
+  char *xattr_buf = xmalloc((size_t)size);
+  size = listxattr(from_file, xattr_buf, (size_t)size);
+  ssize_t tsize = size;
+
+  errno = 0;
+
+  ssize_t max_vallen = 0;
+  char *val = NULL;
+  const char *errmsg = NULL;
+
+  for (int round = 0; round < 2; round++) {
+    char *key = xattr_buf;
+    if (round == 1) {
+      size = tsize;
+    }
+
+    while (size > 0) {
+      ssize_t vallen = getxattr(from_file, key, val, round ? (size_t)max_vallen : 0);
+      // only set the attribute in the second round
+      if (vallen >= 0 && round
+          && setxattr(to_file, key, val, (size_t)vallen, 0) == 0) {
+        //
+      } else if (errno) {
+        switch (errno) {
+        case E2BIG:
+          errmsg = e_xattr_e2big;
+          goto error_exit;
+        case ENOTSUP:
+          errmsg = e_xattr_enotsup;
+          goto error_exit;
+        case ERANGE:
+          errmsg = e_xattr_erange;
+          goto error_exit;
+        default:
+          errmsg = e_xattr_other;
+          goto error_exit;
+        }
+      }
+
+      if (round == 0 && vallen > max_vallen) {
+        max_vallen = vallen;
+      }
+
+      // add one for terminating null
+      ssize_t keylen = (ssize_t)strlen(key) + 1;
+      size -= keylen;
+      key += keylen;
+    }
+    if (round) {
+      break;
+    }
+
+    val = xmalloc((size_t)max_vallen + 1);
+  }
+error_exit:
+  xfree(xattr_buf);
+  xfree(val);
+
+  if (errmsg != NULL) {
+    emsg(errmsg);
+  }
+}
+#endif
+
 // Return a pointer to the ACL of file "fname" in allocated memory.
 // Return NULL if the ACL is not available for whatever reason.
 vim_acl_T os_get_acl(const char *fname)