>From 2b51de993a5444177f537f22a5de926e056b6add Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Fri, 29 May 2015 22:55:25 -0700 Subject: [PATCH 1/2] copy-file now truncates output after writing * src/fileio.c (Fcopy_file): Truncate output after writing rather than before. This is more likely to work than truncation before writing, if the file system is out of space or the user is over disk quota (Bug#20595). Also, check for read errors. --- src/fileio.c | 30 +++++++++++++++++++++++------- 1 file changed, 23 insertions(+), 7 deletions(-) diff --git a/src/fileio.c b/src/fileio.c index 796f08d..a969d3b 100644 --- a/src/fileio.c +++ b/src/fileio.c @@ -1871,8 +1871,6 @@ permissions. */) bool already_exists = false; mode_t new_mask; int ifd, ofd; - int n; - char buf[16 * 1024]; struct stat st; #endif @@ -1974,6 +1972,8 @@ permissions. */) record_unwind_protect_int (close_file_unwind, ofd); + off_t oldsize = 0, newsize = 0; + if (already_exists) { struct stat out_st; @@ -1982,15 +1982,31 @@ permissions. */) if (st.st_dev == out_st.st_dev && st.st_ino == out_st.st_ino) report_file_errno ("Input and output files are the same", list2 (file, newname), 0); - if (ftruncate (ofd, 0) != 0) - report_file_error ("Truncating output file", newname); + if (S_ISREG (out_st.st_mode)) + oldsize = out_st.st_size; } immediate_quit = 1; QUIT; - while ((n = emacs_read (ifd, buf, sizeof buf)) > 0) - if (emacs_write_sig (ofd, buf, n) != n) - report_file_error ("Write error", newname); + while (true) + { + char buf[MAX_ALLOCA]; + ptrdiff_t n = emacs_read (ifd, buf, sizeof buf); + if (n < 0) + report_file_error ("Read error", file); + if (n == 0) + break; + if (emacs_write_sig (ofd, buf, n) != n) + report_file_error ("Write error", newname); + newsize += n; + } + + /* Truncate any existing output file after writing the data. This + is more likely to work than truncation before writing, if the + file system is out of space or the user is over disk quota. */ + if (newsize < oldsize && ftruncate (ofd, newsize) != 0) + report_file_error ("Truncating output file", newname); + immediate_quit = 0; #ifndef MSDOS -- 2.1.0