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Re: [PATCH] Make fsfs survive stale NFS file handles

From: Eric Gillespie <epg_at_pretzelnet.org>
Date: 2007-04-05 18:45:38 CEST

Malcolm Rowe <malcolm-svn-dev@farside.org.uk> writes:

> The rest of the patch looks fine.

Updated patch/message:

In NFS v3 and under, the server doesn't track opened files. If you
unlink(2) or rename(2) a file held open by another process *on the
same host*, that host's kernel typically renames the file to .nfsXXXX
and automatically deletes that when it's no longer open, but this
behavior is not required.

For obvious reasons, this does not work *across hosts*. No one
knows about the opened file; not the server, and not the deleting
client. So the file vanishes, and the reader gets stale NFS file
handle. We have this problem with revprops/* and current.

* subversion/libsvn_fs_fs/fs_fs.c
  (SVN_ESTALE_RETRY_COUNT, SVN_RETRY_ESTALE, SVN_IGNORE_ESTALE): New
  macros for retrying opens and reads after ESTALE, and ignoring
  ESTALE errors from close, within a loop of SVN_ESTALE_RETRY_COUNT
  (10) iterations. SVN_RETRY_ESTALE and SVN_IGNORE_ESTALE are defined
  as SVN_ERR when ESTALE is not defined.

  (read_current): New function for reading the current file using the
  ESTALE macros.

  (get_youngest, get_next_revision_ids): Use read_current.

  (svn_fs_fs__revision_proplist): Use the ESTALE macros.

Index: subversion/libsvn_fs_fs/fs_fs.c
===================================================================
--- subversion/libsvn_fs_fs/fs_fs.c (revision 24424)
+++ subversion/libsvn_fs_fs/fs_fs.c (working copy)
@@ -20,6 +20,7 @@
 #include <string.h>
 #include <ctype.h>
 #include <assert.h>
+#include <errno.h>
 
 #include <apr_general.h>
 #include <apr_pools.h>
@@ -677,6 +678,103 @@
   return SVN_NO_ERROR;
 }
 
+/* SVN_ERR-like macros for dealing with ESTALE
+ *
+ * In NFS v3 and under, the server doesn't track opened files. If you
+ * unlink(2) or rename(2) a file held open by another process *on the
+ * same host*, that host's kernel typically renames the file to
+ * .nfsXXXX and automatically deletes that when it's no longer open,
+ * but this behavior is not required.
+ *
+ * For obvious reasons, this does not work *across hosts*. No one
+ * knows about the opened file; not the server, and not the deleting
+ * client. So the file vanishes, and the reader gets stale NFS file
+ * handle. We have this problem with revprops files and current.
+ *
+ * Wrap opens and reads of such files with SVN_RETRY_ESTALE and closes
+ * with SVN_IGNORE_ESTALE. Call these macros within a loop of
+ * SVN_ESTALE_RETRY_COUNT iterations (though, realistically, the
+ * second try will succeed). Make sure you put a break statement
+ * after the close, at the end of your loop. Immediately after your
+ * loop loop, return err if err.
+ *
+ * You must initialize err to SVN_NO_ERROR, as these macros do not.
+ */
+
+#define SVN_ESTALE_RETRY_COUNT 10
+
+#ifdef ESTALE
+#define SVN_RETRY_ESTALE(err, expr) \
+ { \
+ /* Clear err here (svn_error_clear can safely be passed
+ * SVN_NO_ERROR) rather than after finding ESTALE so we can return
+ * the ESTALE error on the last iteration of the loop. */ \
+ svn_error_clear(err); \
+ err = (expr); \
+ if (err) \
+ { \
+ if (APR_TO_OS_ERROR(err->apr_err) == ESTALE) \
+ continue; \
+ return err; \
+ } \
+ }
+#define SVN_IGNORE_ESTALE(err, expr) \
+ { \
+ svn_error_clear(err); \
+ err = (expr); \
+ if (err) \
+ { \
+ if (APR_TO_OS_ERROR(err->apr_err) != ESTALE) \
+ return err; \
+ } \
+ }
+#else
+#define SVN_RETRY_ESTALE(err, expr) SVN_ERR(expr)
+#define SVN_IGNORE_ESTALE(err, expr) SVN_ERR(expr)
+#endif
+
+/* Long enough to hold: "<svn_revnum_t> <node id> <copy id>\0"
+ * 19 bytes for svn_revnum_t (room for 32 or 64 bit values)
+ * + 2 spaces
+ * + 26 bytes for each id (these are actually unbounded, so we just
+ * have to pick something; 2^64 is 13 bytes in base-36)
+ * + 1 terminating null
+ */
+#define CURRENT_BUF_LEN 48
+
+/* Read the 'current' file FNAME and store the contents in *BUF.
+ Allocations are performed in POOL. */
+static svn_error_t *
+read_current(const char *fname, char **buf, apr_pool_t *pool)
+{
+ apr_file_t *revision_file;
+ apr_size_t len;
+ int i;
+ svn_error_t *err = SVN_NO_ERROR;
+ apr_pool_t *iterpool;
+
+ *buf = apr_palloc(pool, CURRENT_BUF_LEN);
+ iterpool = svn_pool_create(pool);
+ for (i = 0; i < SVN_ESTALE_RETRY_COUNT; i++)
+ {
+ svn_pool_clear(iterpool);
+
+ SVN_RETRY_ESTALE(err, svn_io_file_open(&revision_file, fname,
+ APR_READ | APR_BUFFERED,
+ APR_OS_DEFAULT, iterpool));
+
+ len = CURRENT_BUF_LEN;
+ SVN_RETRY_ESTALE(err, svn_io_read_length_line(revision_file,
+ *buf, &len, iterpool));
+ SVN_IGNORE_ESTALE(err, svn_io_file_close(revision_file, iterpool));
+
+ break;
+ }
+ svn_pool_destroy(iterpool);
+
+ return err;
+}
+
 /* Find the youngest revision in a repository at path FS_PATH and
    return it in *YOUNGEST_P. Perform temporary allocations in
    POOL. */
@@ -685,22 +783,12 @@
              const char *fs_path,
              apr_pool_t *pool)
 {
- apr_file_t *current_file;
- char buf[81];
- apr_size_t len;
+ char *buf;
 
- SVN_ERR(svn_io_file_open(&current_file,
- svn_path_join(fs_path, PATH_CURRENT, pool),
- APR_READ, APR_OS_DEFAULT, pool));
-
- len = sizeof(buf) - 1;
- SVN_ERR(svn_io_file_read(current_file, buf, &len, pool));
- buf[len] = '\0';
+ SVN_ERR(read_current(svn_path_join(fs_path, PATH_CURRENT, pool), &buf, pool));
   
   *youngest_p = SVN_STR_TO_REV(buf);
   
- SVN_ERR(svn_io_file_close(current_file, pool));
-
   return SVN_NO_ERROR;
 }
 
@@ -1521,25 +1609,48 @@
 {
   apr_file_t *revprop_file;
   apr_hash_t *proplist;
- svn_error_t *err;
+ svn_error_t *err = SVN_NO_ERROR;;
+ int i;
+ apr_pool_t *iterpool;
 
- err = svn_io_file_open(&revprop_file, path_revprops(fs, rev, pool),
- APR_READ | APR_BUFFERED, APR_OS_DEFAULT, pool);
- if (err && APR_STATUS_IS_ENOENT(err->apr_err))
+ iterpool = svn_pool_create(pool);
+ for (i = 0; i < SVN_ESTALE_RETRY_COUNT; i++)
     {
+ svn_pool_clear(iterpool);
+
+ /* Clear err here (svn_error_clear can safely be passed
+ * SVN_NO_ERROR) rather than after finding ESTALE so we can
+ * return the ESTALE error on the last iteration of the loop. */
       svn_error_clear(err);
- return svn_error_createf(SVN_ERR_FS_NO_SUCH_REVISION, NULL,
- _("No such revision %ld"), rev);
- }
- else if (err)
- return err;
+ err = svn_io_file_open(&revprop_file, path_revprops(fs, rev, iterpool),
+ APR_READ | APR_BUFFERED, APR_OS_DEFAULT, iterpool);
+ if (err)
+ {
+ if (APR_STATUS_IS_ENOENT(err->apr_err))
+ {
+ svn_error_clear(err);
+ return svn_error_createf(SVN_ERR_FS_NO_SUCH_REVISION, NULL,
+ _("No such revision %ld"), rev);
+ }
+#ifdef ESTALE
+ else if (APR_TO_OS_ERROR(err->apr_err) == ESTALE)
+ continue;
+#endif
+ return err;
+ }
 
- proplist = apr_hash_make(pool);
+ proplist = apr_hash_make(pool);
 
- SVN_ERR(svn_hash_read(proplist, revprop_file, pool));
+ SVN_RETRY_ESTALE(err, svn_hash_read(proplist, revprop_file, pool));
 
- SVN_ERR(svn_io_file_close(revprop_file, pool));
+ SVN_IGNORE_ESTALE(err, svn_io_file_close(revprop_file, iterpool));
 
+ break;
+ }
+ if (err)
+ return err;
+ svn_pool_destroy(iterpool);
+
   *proplist_p = proplist;
 
   return SVN_NO_ERROR;
@@ -3766,17 +3877,11 @@
                       svn_fs_t *fs,
                       apr_pool_t *pool)
 {
- apr_file_t *revision_file;
- char buf[80];
- apr_size_t len;
+ char *buf;
   char *str, *last_str;
 
- SVN_ERR(svn_io_file_open(&revision_file, svn_fs_fs__path_current(fs, pool),
- APR_READ | APR_BUFFERED, APR_OS_DEFAULT, pool));
+ SVN_ERR(read_current(svn_fs_fs__path_current(fs, pool), &buf, pool));
 
- len = sizeof(buf);
- SVN_ERR(svn_io_read_length_line(revision_file, buf, &len, pool));
-
   str = apr_strtok(buf, " ", &last_str);
   if (! str)
     return svn_error_create(SVN_ERR_FS_CORRUPT, NULL,
@@ -3796,8 +3901,6 @@
 
   *copy_id = apr_pstrdup(pool, str);
 
- SVN_ERR(svn_io_file_close(revision_file, pool));
-
   return SVN_NO_ERROR;
 }
 

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Received on Thu Apr 5 18:46:50 2007

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